Which of the following cannot be used as standard solution for determination of cell constant of conductivity cell?

Which from following reagents is used in the conversion of phenol to picric acid?

Which element from following has largest atomic size as compared to other three?

Calculate the enthalpy change when 12 g carbon react with sufficient hydrogen to form methane. If enthalpy of formation of methane is $-75 \mathrm{~kJ} \mathrm{~mol}^{-1}$.