The volume of oxygen required for complete combustion of 0.25 mole of methane at STP is

A solution of $$\mathrm{CuSO}_4$$ is electrolysed using a current of 1.5 amperes for 10 minutes. What mass of Cu is deposited at cathode? [Atomic mass of $$\mathrm{Cu}=63.7$$]

Which of the following reaction proves the chlorinating property of phosphorus pentachloride?

Number of oxygen atoms present in salicylaldehyde are