During the radioactive decay of a substance,which of the following is $NOT$ emitted?

The ${ }_{92}^{235} U$ atom disintegrates to ${ }_{82}^{207} Pb$ with a half-life of $10^9 \ yr$. In the process,it emits $7 \ \alpha$ particles and $n \ \beta^{-}$ particles. Here,$n$ is

$A$ free neutron decays spontaneously into:

The decay of a proton to a neutron is:

$A$ radioactive material $P$ first decays into $Q$ and then $Q$ decays to non-radioactive material $R$. Which of the following figures represents the time-dependent mass of $P$,$Q$,and $R$?

In the emission of $\gamma$-rays from a nucleus: