Write the equation for controlled oxidation of methane to form formaldehyde.

Write the equation for controlled oxidation of methane to form formic acid.

Write balanced chemical equation when a mixture of methane and oxygen (in the volume ratio $9:1$) is passed through a copper tube at $200°\mathrm{C}$ and $100 \mathrm{atm}$.

Write balanced chemical equation when a mixture of methane and oxygen is heated in the presence of a metallic oxide which acts as a catalyst.

Write balanced chemical equation when a mixture of methane and air is heated at $473 \mathrm{K}$ and $130 \mathrm{atm}$.