Which of the following cannot be emitted by radioactive substances during their decay?

$A$ radioactive nucleus is initially at rest. It decays by emitting an electron and a neutrino at right angles to each other. The momentum of the electron is $3.2 \times 10^{-23} \ kg \cdot m/s$ and the momentum of the neutrino is $6.4 \times 10^{-23} \ kg \cdot m/s$. What is the direction of the recoil of the nucleus with respect to the direction of the electron?

In the given nuclear reaction,$A, B, C, D, E$ represent:
$_{92}U^{238} \xrightarrow{\alpha} _{B}Th^{A} \xrightarrow{\beta} _{D}Pa^{C} \xrightarrow{E} _{92}U^{234}$

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

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

When ${}_{92}U^{238}$ changes into ${}_{82}Pb^{206}$,the number of $\alpha$ and $\beta^-$ particles emitted are: