the density of methane at 2 atmosphere pressure at 25 degree centigrade is how many gram per litre?

For methane gas (CH₄) :
Pressure, P = 2 atm
Absolute temperature, T = (273 + 25) K = 298 K
Gas constant, R = 0.0821 atm L / (mol K)
Molar mass, M = (12.01 + 1.008×4) g/mol = 16.04 g/mol
Density, d = ? g/L

PV = nRT and n = m/M
Then, PV = (m/M)RT
Rearrange: m/V = PM/(RT)
But d = m/V, then: d = PM/(RT)

Density, d
= (2 atm) × (16.04 g/mol) / {[0.0821 atm L/ (mol K)] × (298 K)}
= 1.31 g/L