Answer : The correct option is, (2) ethyl
Explanation :
As per IUPAC rules,
For the number of carbon atom, we add prefix as 'meth' for 1, 'eth' for 2, 'prop' for 3, 'but' for 4, 'pent' for 5, 'hex' for 6, 'sept' for 7, 'oct' for 8, 'nona' for 9 and 'deca' for 10.
A suffix '-ane' is added at the end of the name.
If two of more similar alkyl groups are present, then the words 'di', 'tri' 'tetra' and so on are used to specify the number of times these alkyl groups appear in the chain.
In the given organic formula, the group given the box have 2 carbon chain which named as ethyl.
Hence, the correct option is, (2) ethyl