Among the following reactions, incomplete combustion of methane is-

1. \(2 \mathrm{CH}_4+\mathrm{O}_2 \xrightarrow[]{\mathrm{Cu/523 \ K/100 \ atm}} 2 \mathrm{CH}_3 \mathrm{OH}\)
2. \(\mathrm{CH}_4+\mathrm{O}_2 \xrightarrow[]{\mathrm{Mo_{2}O_{3}}} \mathrm{HCHO}+\mathrm{H}_2 \mathrm{O}\)
3. CH4 + O2 → C + 2H2O
4.  CH4 + 2O2 → CO2 + 2H2O

HINT: Incomplete combustion forms carbon black.
During incomplete combustion of alkanes with insufficient amount of air or dioxygen carbon black is formed which is used in the manufacturing of ink, printer ink, black pigments and as filters. Thus,

The incomplete combustion of methane can result in a slew of partially oxidized products, including COCO, but also methanol, formic acid, formaldehyde, and higher hydrocarbons also.

However,the oxidation of methane to soot is generally given as the following: