Answer:
2. A mnemonic device.
Explanation:
A mnemonic device helps us retain and remember large amount of information we've learnt, by putting it in a fun way easy for us to recall. A mnemonic device that uses the first letters of words in a sentence to form another sentence or rhyme is called an acrostic.
Mnemonics are one of the many memory tools out there that aid students with information retention and retrieval.
Examples of popular mnemonics include;
1) BODMAS which stands for Brackets, Of, Division, Multiplication, Addition, Subtraction. This signifies the order of preference in mathematical calculations.
2) ROY G BIV which stands for Red, Orange, Yellow, Green, Blue, Indigo, and Violet.