In an elastic collision of two particles,which of the following is conserved?

$A$ body of mass $1 ~g$ and carrying a charge $10^{-8} ~C$ passes through two points $P$ and $Q$. $P$ and $Q$ are at electric potentials $600 ~V$ and $0 ~V$,respectively. The velocity of the body at $Q$ is $20 ~cm/s$. Its velocity in $m/s$ at $P$ is:

Which one of the following molecules contains both ionic and covalent bonds?

The dipole moment order of which of the following pairs of molecules is $NOT$ correct?

With which of the following does hydrogen combine directly?

$A$ ball moving with velocity $2 \ m/s$ collides head-on with another stationary ball of double the mass. If the coefficient of restitution is $0.5$,then their velocities (in $m/s$) after collision will be