Which of the following is the correct IUPAC name of given organic compound (X)?

The structure of compound (X) contains a four-carbon chain with one $$C=C$$ double bond, a bromine atom attached to an end carbon, and a methyl substituent on the vinylic carbon.

Step 1 - Select the parent chain
Choose the longest continuous chain that includes the double bond. It has four carbons, so the word-root is “but” and, with one double bond, the principal suffix is “-ene”.

Step 2 - Number the parent chain
According to IUPAC rules, give the double bond the lowest possible locant. Numbering from the bromine-bearing end gives:

• C-1 → Br
• C-2 → first carbon of the $$C=C$$ bond and also bears the methyl group
• C-3 → second carbon of the $$C=C$$ bond
• C-4 → terminal carbon

This locates the double bond at $$2$$ (but-2-ene), bromine at $$1$$, and the methyl substituent at $$2$$. If we numbered from the opposite end, the double bond would still start at $$2$$, but bromine would be at $$4$$; because 1 < 4, the first numbering is preferred.

Step 3 - Assemble the name
List substituents alphabetically before the parent name and insert their locants:

Bromo (locant 1) precedes methyl (locant 2), followed by the parent “but-2-ene”.

The IUPAC name is $$\text{1-Bromo-2-methylbut-2-ene}$$.

Hence, the correct choice is Option C which is: 1-Bromo-2-methylbut-2-ene.