The water gas on reacting with cobalt as a catalyst forms

Water gas is a mixture of carbon monoxide ($$CO$$) and hydrogen ($$H_2$$), produced by passing steam over hot coke:

$$C + H_2O \rightarrow CO + H_2$$

When water gas is passed over a cobalt ($$Co$$) catalyst under appropriate conditions of temperature and pressure, it produces methanoic acid (formic acid).

The balanced reaction is:

$$CO + H_2O \rightarrow HCOOH$$

Here, carbon monoxide reacts with water (present as steam) in the presence of a cobalt catalyst to form methanoic acid ($$HCOOH$$).

Let us verify why the other options are incorrect:

Option A (Methanal / Formaldehyde, $$HCHO$$): Methanal is obtained by catalytic oxidation of methanol using a silver or iron-molybdenum oxide catalyst. It is not a direct product of water gas with a cobalt catalyst.

Option C (Ethanol, $$C_2H_5OH$$): Ethanol can be produced from syngas but requires different catalysts (such as rhodium-based catalysts) and specific conditions. Cobalt catalyst does not directly produce ethanol from water gas.

Option D (Methanol, $$CH_3OH$$): Methanol is produced from syngas ($$CO + 2H_2$$) using a $$ZnO$$-$$Cr_2O_3$$ catalyst at high pressure. The reaction is $$CO + 2H_2 \rightarrow CH_3OH$$. This requires a different catalyst, not cobalt.

Therefore, the correct answer is Option B: Methanoic acid.