$PbO_2$ reacts with concentrated $HNO_3$. The gas evolved is:

The catenation tendency of $C, Si$ and $Ge$ is in the order $Ge < Si < C$. The bond energies (in $kJ \ mol^{-1}$) of $C-C, Si-Si$ and $Ge-Ge$ bonds,respectively,are:

Give the use of diamond.

Name the type of silicate structure in which one oxygen atom of $SiO_4^{4-}$ is shared with another silicate unit.

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Carbon forms two important oxides $- CO$ and $CO_2$. $CO$ is neutral whereas $CO_2$ is acidic in nature.
Reason $R$: $CO_2$ can combine with water in a limited way to form carbonic acid,while $CO$ is sparingly soluble in water.
In the light of the above statements,choose the most appropriate answer from the options given below:

$P_2O_5$ is used extensively as a