When two species of different genealogy come to resemble each other as a result of adaptation,the phenomenon is termed as

$A$ radioactive nucleus $A$ with a half-life $T$ decays into a nucleus $B$. At $t = 0$,there is no nucleus $B$. At some time $t$,the ratio of the number of $B$ to that of $A$ is $0.3$. Then,$t$ is given by:

If $x^2+\alpha y^2+2 \beta y=a^2$ represents a pair of perpendicular lines,then $\beta$ equals to

$\operatorname{sech}^{-1}(\sin \theta)$ is equal to

The radius of the circle $r = 12 \cos \theta + 5 \sin \theta$ is

In $chloroethane$,the carbon bearing halogen is bonded to $...$ hydrogen $(s)$. It is called $......$ alkyl halide.