Which of the following physical quantities is measured using the unit $rad$?

$A$ certain radioactive material can undergo three different types of decay,each with a different decay constant $\lambda_1$,$\lambda_2$,and $\lambda_3$. Then the effective decay constant is:

If $_{92}U^{238} \to _{Z}X^{A} + _{2}He^{4}$,then $Z$ and $A$ will be ..........

$A$ nucleus $X$ emits a beta particle to produce a nucleus $Y$. If their atomic masses are $M_{x}$ and $M_{y}$ respectively, the maximum energy of the beta particle emitted is (where $m_{e}$ is the mass of an electron and $c$ is the velocity of light):

In the given radioactive decay,the number of $\alpha$ and $\beta$ particles emitted are respectively: $_{90}X^{200} \rightarrow _{80}Y^{168}$

For the $\beta^{+}$ (positron) emission from a nucleus,there is another competing process known as electron capture (an electron from an inner orbit,say,the $K$-shell,is captured by the nucleus and a neutrino is emitted).
$_{z}^{A} X + e^{-} \rightarrow _{z-1}^{A} Y + \nu$
Show that if $\beta^{+}$ emission is energetically allowed,electron capture is necessarily allowed,but not vice-versa.