Out of the following,choose the ray which does not travel with the velocity of light.

The $\beta$-particles of a radioactive metal originate from

Alpha rays emitted from a radioactive substance are:

When a radioactive substance emits an $\alpha$-particle,its position in the periodic table is lowered by

What happens to the mass number and atomic number of an element when it emits $\gamma$-radiation?

$A$ radioactive element ${ }_{92}^{242} X$ emits two $\alpha$ particles,one electron and two positrons. The product nucleus is represented by ${ }_{P}^{234} Y$. The value of $P$ is