Which of the following represents the correct IUPAC name for the compounds concerned?

1. 2,2-Dimethylpentane Or 2-Dimethylpentane

This is correct IUPAC name.

2. 2,4,7-Trimethyloctane Or 2,5,7-Trimethyloctane

2,4,7-Trimethyloctane is correct IUPAC name because methyl group has lowest priority.

C) 2-cloro 4 methyl pentane  Or  4-cloro-2 methyl pentane

2-   Chloro   4  methyl  pentane  is  correct  IUPAC  name because Clorine has lowest priority than methyl.

 D) But-3-yne-1-ol   Or   But-4-ol-1-yne 

But-3-yne-1-ol   is correct IUPAC name because OH   group has lowest priority and after that next priority to alkyne group.