The mass of oxygen required for the complete combustion of 1.6 kg of methane is

The mass of oxygen required for the complete combustion of 1.6 kg of methane is 6.4 kg.
 

The molecular mass of methane = $C{H}_4$= 16 g 

The following is the combustion reaction of methane,

${\mathrm{CH}}_4 + 2 {\mathrm{O}}_2 \stackrel{∆}{\to } {\mathrm{CO}}_2 + 2 {\mathrm{H}}_2\mathrm{O}$

The mass of methane molecule is 16 g.
The mass of oxygen molecule is 32g.
2 molecules of oxygen are used for the combustion of 1 molecule of methane.

Hence, the amount of oxygen required for the complete combustion of 16 g of methane = $32 \times 2=64 \mathrm{g}$

So, the amount of oxygen required for the complete combustion of 1.6 kg of methane$=\frac{Mass of O_2 }{Mass of C{H}_4}\times Amount of C{H}_4=\frac{64 \times 1.6}{16}= 6.4 kg$