Which of the following is monoatomic?

Identify $X$ in the following sequence of reaction:
$C_6H_5-Cl$ $\xrightarrow[CuCN]{KCN} P$ $\xrightarrow{LiAlH_4} Q$ $\xrightarrow{HNO_2} X$

In a mass spectrometer used for measuring the masses of ions,the ions are initially accelerated by an electric potential $V$ and then made to describe semicircular paths of radius $R$ using a magnetic field $B$. If $V$ and $B$ are kept constant,the ratio $\left( \frac{\text{charge on the ion}}{\text{mass of the ion}} \right)$ will be proportional to

Which of the following sulfates is insoluble in water?

The synthesis of $ATP$ in photosynthesis and respiration is essentially an oxidation-reduction process involving the removal of energy from:

Two particles $A$ and $B$ initially at rest move towards each other under a mutual force of attraction. At the instant when the speed of $A$ is $v$ and the speed of $B$ is $2v$,the speed of the centre of mass of the system is