Which of the following can pass through $20 \, cm$ thickness of steel?

In a radioactive reaction $_{92}X^{232} \to _{82}Y^{204}$,the number of $\alpha$-particles emitted is:

In radioactive decay process,the negatively charged emitted $\beta$-particles are

$A$ radioactive nucleus emits $4 \alpha$ particles and $7 \beta$ particles in succession. The ratio of the number of neutrons to that of protons in the final nucleus is $[A = \text{mass number}, Z = \text{atomic number}]$

An isotope of the original nucleus can be formed in a radioactive decay,with the emission of which of the following particles?

$A$ nucleus $_n^mX$ emits one $\alpha$ particle and two $\beta^-$ particles. The resulting nucleus is