What is the name of this hydrocarbon?

The name of the hydrocarbon is but-2-yne or 2-butyne.

Explanation:

1. While naming the organic compound, we will see longest carbon chain in molecule and number it.Here, the longest carbon chain is of 4 carbon atoms.

Prefix for the chain of 4 carbon atoms is 'But'.

2. After that we number the chain from the side where smallest number falls on functional group or double or triple bond coming in the chain.

If there is any unsaturation in the molecule like presence of double bond or triple bond in the carbon -carbon atom:

Here , triple bond is present between the second and third atom so the name of the molecule will be: But-2-yne.

The name of the hydrocarbon is but-2-yne or 2-butyne.