What amount of oxygen is used at S.T.P. to obtain 9 g water from sufficient amount of hydrogen gas?

A solution of 6 g of solute in 100 g of water boils at 100.52$$^\circ$$C. The molal elevation constant of water is 0.52 K kg mol$$^{-1}$$. What is molar mass of solute?

Which among the following compounds has highest melting point?

Instantaneous rate of a reaction is $$ - {1 \over 2}{{d[x]} \over {dt}} = - {{d[y]} \over {dt}} = {1 \over 2}{{d[z]} \over {dt}}$$, identify the reaction.