$A$ soft heavy metal melts at $30\ ^oC$ and is used in making heat-sensitive thermometers. The metal is:

Which of the following oxides does not form an acidic aqueous solution?

Which of the following is a tetrabasic acid?

Chemical nature of the nitrogen oxide compound obtained from a reaction of concentrated nitric acid and $P_{4}O_{10}$ (in $4:1$ ratio) is:

The bond energies (in $kJ \ mol^{-1}$) of $N-H$,$P-H$,and $As-H$ are respectively:

The three important oxidation states of phosphorus are