In a binary compound,atoms of element $A$ form a $hcp$ structure and those of element $M$ occupy $2/3$ of the tetrahedral voids of the $hcp$ structure. The formula of the binary compound is

Under the influence of a uniform magnetic field,a charged particle is moving in a circle of radius $R$ with constant speed $v$. The time period of the motion

The electric resistance of a certain wire of iron is $R$. If its length and radius are both doubled,then

The logarithm of $32\sqrt[5]{4}$ to the base $2\sqrt{2}$ is:

$(\tan ^{-1} x)^2+(\cot ^{-1} x)^2=\frac{5 \pi^2}{8} \Rightarrow x=$

$A$ metal $M$ and its compound can give the following observable changes in a sequence of reactions: $M$ $\xrightarrow{\text{dil. } HNO_3} M(NO_3)_2$ $\xrightarrow{NaOH} \text{White ppt.}$ $\xrightarrow{\text{Excess } NaOH} \text{Colourless solution}$ $\xrightarrow{H_2S} \text{White ppt.}$. Identify the metal $M$.