Which classification system was proposed by $R.H. Whittaker$?

$AB$ crystallizes in a body-centred cubic lattice with edge length '$a$' equal to $387 \ pm$. The distance between two oppositely charged ions in the lattice is ............. $pm$.

$\lim _{x \rightarrow 0} x^2 \sin \left(\frac{\pi}{x}\right)$ is equal to

$A$ closed hollow insulated cylinder is filled with gas at $0^{\circ} C$ and also contains an insulated piston of negligible weight and negligible thickness at the middle point. The gas in one side of the piston is heated to $100^{\circ} C$. If the piston moves $5 ~cm$, the total length of the hollow cylinder is: (in $~cm$)

In the circuit,if the forward voltage drop for the diode is $0.5\, V$,the current will be.......$mA$.

During the mean life of a radioactive element,the fraction that disintegrates is