In the nuclear reaction,${ }_6^{11} C \rightarrow{ }_5^{11} B + \beta^+ + X$,$X$ stands for

For the radioactive nuclei that undergo either $\alpha$ or $\beta$ decay, which one of the following cannot occur?

The radioactive decay of uranium into thorium is expressed by the equation $_{92}^{238}U \to _{90}^{234}Th + X,$ where $X$ is

The nucleus ${ }_{Z}^{A} X$ undergoes the series of reactions given below:
${ }_{Z}^{A} X \stackrel{\alpha \text {-decay }}{\longrightarrow} P \stackrel{\beta \text {-decay }}{\longrightarrow} Q \stackrel{\alpha \text {-decay }}{\longrightarrow} R$
The number of neutrons in the nucleus $R$ is

In the following nuclear reaction,$x$ stands for: $n \rightarrow p + e^{-} + x$

Which of the following will have the highest penetrating power?