After the emission of one $\alpha$-particle followed by one $\beta$-particle from the atom of $_{92}X^{238}$,the number of neutrons in the atom will be

After the emission of an $\alpha$-particle from the atom $_{92}X^{238}$,the number of neutrons in the resulting atom will be:

Identify $[A]$ and $[B]$ in the following reaction sequence:
${ }_{89}^{227} Ac$ $\xrightarrow{-\beta} [A]$ $\xrightarrow{-\alpha} [B]$ $\xrightarrow{-\alpha} { }_{86}^{219} Rn$

The radiations from a naturally occurring radio element,as seen after deflection in a magnetic field in one direction,are

Which is not emitted by a radioactive substance?

Which has the least penetrating power?