Nitrogen gas is absorbed by which of the following substances at high temperature to form a cyanamide derivative?

Correct statements among $(i)$ to $(iv)$ regarding silicones are:
$(i)$ they are polymers with hydrophobic character
$(ii)$ they are biocompatible
$(iii)$ in general,they have high thermal stability and low dielectric strength
$(iv)$ usually they are resistant to oxidation and used as greases.

Which one of the following oxides is neutral?

Which of the following,on reaction with water,will have a $pH$ less than $7$?

Which of the following halides does not undergo hydrolysis?

$P_2O_5$ is used extensively as a