The reagent(s) for the following conversion,

The number of structural isomers for C$$_6$$H$$_{14}$$ is :

The percentage of p-character in the orbitals forming P-P bonds in P$$_4$$ is

When 20 g of naphthoic acid (C$$_{11}$$H$$_{8}$$O$$_{2}$$) is dissolved in 50 g of benzene in 50 g of benzene (K$$_f$$ = 1.72 K kg mol$$^{-1}$$), a freezing point depression of 2 K is observed. The van't Hoff factor (i) is :