Coding & Computers

Why C? And why not the others?

Correct answer: C. Because the tiny electronic switches inside a computer chip are far more reliable when built to represent just two clear states, like off and on, than when built to reliably tell apart ten finely graded voltage levels

Computer chips are built from millions of transistors, tiny electronic switches that work best when they only ever need to represent two clearly distinguishable states, such as 'on' (current flowing) and 'off' (no current). Building hardware that could reliably tell apart ten different voltage levels for ten decimal digits would be far more complex and error-prone than hardware that only has to distinguish two states, so binary became the natural fit for how physical circuits actually work. The option about typing convenience is wrong because the choice of binary has nothing to do with what is easy for a human to type; programmers rarely type raw binary at all, they write in higher-level languages that get translated down to binary. The option about storage space is wrong because representing the same value in binary generally takes more digits than in decimal, not fewer, so binary is not chosen to save space. The option about human eyesight is wrong because a computer's internal binary representation is never about what a human perceives on a screen; the digits 0 and 1 describe internal electrical states, not visible symbols.

Source: BBC Bitesize GCSE Computer Science: Systems architecture and data representation

Why A? And why not the others?

Correct answer: A. Only when both of its inputs are 1

An AND gate is a basic logic gate used to combine two conditions so that the overall result is only true when both conditions hold, which is why it outputs 1 only when both of its inputs are 1; for any other combination of inputs, its output is 0. This makes it useful for things like 'let the player through only if they have a key AND they have enough energy'. The option describing an output of 1 whenever at least one input is 1 actually describes an OR gate, which is far more permissive and has a completely different truth table from AND. The option describing an output of 1 when exactly one input is 1 but not both describes an XOR (exclusive OR) gate, which specifically excludes the both-true case that AND requires. The option about reacting to any input change is not how a basic AND gate works at all; a plain AND gate has no memory of previous values and depends only on the current values of its inputs, not on whether they changed.

Source: BBC Bitesize GCSE Computer Science: Boolean logic

Why D? And why not the others?

Correct answer: D. RAM is volatile memory that needs a constant electrical charge to hold data, so it clears when power is lost, while storage devices like hard drives and SSDs retain data without power

RAM is volatile memory, meaning it only holds its data while it keeps receiving electrical power; the moment power is cut, whatever was stored in RAM is lost, which is why an unsaved document vanishes after a full power-off. Long-term storage devices like hard drives (which store data as magnetic patterns) and SSDs (which store data in flash memory cells that hold their charge state) are non-volatile, so the data they hold survives with no power at all, which is why saved photos are still there afterwards. The option about physical location is wrong because RAM usually sits on its own chip on the motherboard rather than inside the CPU, and plenty of storage, like an internal SSD, is not an external accessory at all. The option about data type is wrong because RAM can temporarily hold any kind of binary data, including images and video, while a program is actively using them; the real distinction is about whether the data survives a power loss, not what type of data it is. The option about internet connectivity is wrong because both RAM and storage function perfectly well with no internet connection whatsoever; volatility has nothing to do with networking.

Source: BBC Bitesize GCSE Computer Science: Memory

Why B? And why not the others?

Correct answer: B. Decomposition

Decomposition is the computational-thinking skill of breaking a large, complicated problem down into smaller, more manageable sub-problems, each of which is easier to design, write, and test on its own before being combined into the finished program, which is exactly what splitting a recipe app into 'search', 'display', and 'save favourite' pieces does. It is taught alongside other computational-thinking skills like abstraction and pattern recognition because it makes large projects manageable. The option describing encryption is wrong because encryption is about scrambling data so it can only be read by someone with the right key, which has nothing to do with structuring a programming problem. The option describing compilation is wrong because compilation is the separate process of translating finished source code into machine code the computer can run, which happens after the code is written, not a technique for planning how to divide up a problem. The option describing debugging is wrong because debugging means finding and fixing errors in code that already exists, which is a later step in development, not the initial act of splitting a problem into smaller parts.

Source: BBC Bitesize GCSE Computer Science: Computational thinking - decomposition

Why A? And why not the others?

Correct answer: A. Opening the middle page each time and eliminating half the remaining pages at every step, because the pages are already sorted alphabetically, quickly narrows down where the name must be

This is binary search: because the pages are already sorted alphabetically, comparing the wanted name to the name on the middle page tells you immediately which half of the remaining pages the name must be in, so that whole half can be thrown away in one step; repeating this halves the remaining pages each time, so a 1,000-page book needs only about ten comparisons rather than up to a thousand. The option describing one-by-one checking as needing to already know the exact page is backwards; that requirement describes nothing about linear search, and binary search actually works precisely because you do not know the page in advance, narrowing it down step by step instead. The option claiming halving works the same whether or not pages are sorted is wrong because without a sorted order there is no way to know which half contains the name, so the middle-page trick would not reliably eliminate the right half at all. The option claiming both methods take a similar number of steps is wrong by a huge margin: one-by-one checking can need up to 1,000 steps in the worst case, while halving needs only around ten, an enormous practical difference at this scale.

Source: BBC Bitesize GCSE Computer Science: Searching algorithms

Why C? And why not the others?

Correct answer: C. Bug

On 9 September 1947, the team working with Grace Hopper on Harvard's Mark II computer traced a relay malfunction to a moth caught inside the mechanism; they taped the moth into their logbook next to the note 'first actual case of bug being found', and this vivid, well-documented incident is credited with popularising 'bug' as the word for a fault that makes a computer misbehave (the logbook page, moth and all, is preserved by the Smithsonian). The word 'bug' for a technical flaw actually existed even earlier, notably used by Thomas Edison decades before, but this 1947 moth is the famous moment tied to computing specifically. The option naming 'byte', a unit of eight bits, is wrong because that word was coined separately by engineer Werner Buchholz in 1956 and has no connection to this incident. The option naming 'glitch' is wrong because that word's origins trace to 1960s engineering and aerospace slang, unrelated to a 1947 relay and moth. The option naming 'crash', meaning a sudden program or system failure, is wrong because it describes total failure to run at all, not a specific, traceable physical fault like this one, and has no link to this particular story either.

Source: Smithsonian National Museum of American History: 'Log Book With Computer Bug' object record

Why D? And why not the others?

Correct answer: D. 65

ASCII (American Standard Code for Information Interchange), finalised in the 1960s, assigns every standard keyboard character a unique number so it can be stored and processed as binary; the uppercase letter 'A' is assigned the number 65, with the rest of the uppercase alphabet following consecutively from there ('B' is 66, 'C' is 67, and so on). The option giving 97 is a genuine ASCII code, but for the lowercase letter 'a', not the uppercase 'A'; the lowercase letters sit exactly 32 higher than their uppercase counterparts, which is why code can switch case just by adding or subtracting 32. The option giving 48 is also a real ASCII code, but for the printable digit character '0', an entirely different symbol from any letter. The option giving 13 is the ASCII code for carriage return, a control character used to mark the start of a new line on old teletype printers, not a printable letter at all.

Source: BBC Bitesize GCSE Computer Science: Data representation - character sets

Why B? And why not the others?

Correct answer: B. A variable is a named container that stores a value which can be read and changed while the program runs, letting 'score' hold different numbers at different points in the game

A variable is a named storage location whose value can be read and updated while a program runs; 'score = 0' creates the variable and gives it a starting value, and 'score = score + 10' later reads the current value, adds ten to it, and stores the updated result back under the same name, which is only possible because a variable's contents are allowed to change over time. The option describing a value that can never change once set actually describes a constant, the opposite of what this example shows, since 'score' clearly changes as points are earned. The option describing a comment is wrong because comments are notes for human readers that the computer skips entirely when running the code, and they never store or affect any value like a score. The option describing an instruction to display a value is wrong because that describes an output or print statement, which shows a value on screen but does not itself store or update any data the way a variable does.

Source: BBC Bitesize GCSE Computer Science: Programming fundamentals - variables

Why C? And why not the others?

Correct answer: C. It swaps the two neighbouring elements, then continues comparing the next pair further along the list

Bubble sort moves left to right through a list comparing each pair of neighbouring elements one at a time; whenever the left element is greater than the right one (for ascending order), it swaps just those two neighbours and then carries straight on to compare the next adjacent pair further along, repeating full passes over the list until an entire pass completes with no swaps, at which point the list is sorted, with larger values gradually 'bubbling' toward the end across successive passes. The option describing removing an element is wrong because sorting never deletes anything; every element that starts in the list is still present at the end, only rearranged. The option describing moving the smaller element all the way to the front in one step is wrong because bubble sort only ever swaps two adjacent elements per comparison, it never relocates an element across the whole list in a single move. The option describing stopping and restarting from the beginning is wrong because bubble sort does not abandon a pass after a swap; it keeps comparing forward along the same pass, only beginning a fresh pass once it reaches the end of the list.

Source: BBC Bitesize GCSE Computer Science: Sorting algorithms - bubble sort

Why A? And why not the others?

Correct answer: A. Writing what is widely considered the first published algorithm intended to be carried out by a machine, for computing a sequence of Bernoulli numbers

Lovelace's 1843 notes on Babbage's proposed Analytical Engine included a detailed, step-by-step method for the machine to compute a sequence of Bernoulli numbers, which is widely regarded by historians of computing as the first algorithm ever published for execution by a machine; she also wrote about the idea that such a machine could one day manipulate more than numbers alone, including symbols and music, which is why she is often credited as the first computer programmer. The option about physically building a working computer is wrong because the Analytical Engine was never completed in either Babbage's or Lovelace's lifetime; no full working machine of that design existed at the time, and Lovelace's own contribution was mathematical and written, not mechanical construction. The option about inventing binary is wrong because the binary number system was formalised by the mathematician Gottfried Leibniz in the seventeenth century, long before either Lovelace or Babbage worked on the Analytical Engine. The option about coining the word 'computer' is wrong because that word originally referred to human beings who performed calculations by hand for centuries before Lovelace's time, only later shifting to mean a machine.

Source: Encyclopaedia Britannica: 'Ada Lovelace' biography