Which of the following compounds has the lowest melting point?

If $|a| < 1$ and $b = \sum_{k=1}^{\infty} \frac{a^k}{k}$,then $a$ is equal to

Diazo-coupling is useful to prepare some

Which one of the following statements is correct with respect to basic character?

$A$ satellite is revolving very close to a planet of density $\rho$. The period of revolution of the satellite is

Statement $-1$ : $\sim (p \leftrightarrow \sim q)$ is equivalent to $p \leftrightarrow q$.
Statement $-2$ : $\sim (p \leftrightarrow \sim q)$ is a tautology.