The number of structural isomers for ${\mathrm{C}}_6{\mathrm{H}}_{14}$ are

The product expected to be formed in a Wurtz reaction of a mixture of neopentyl bromide and isobutyl bromide are

(i) $2,2,4-$trimethylpentane

(ii) $2,2,5,5-$tetramethylhexane

(iii) $2,2,4,4-$tetramethylhexane

(iv) $2,5-$dimethylhexane

(v) $2,2,5-$trimethylhexane

Cycloalkane formed when $1,4-$dibromopentane is heated with sodium is