A gas has a pressure of 6.46atm at 227 degrees Celsius. What will it’s pressure be at 27 degree Celsius, if the volume is held constant?

Initial: P₁ = 6.46 atm, T₁ = (273 + 227) K = 500 K
Final: P₂ = ? atm, T₂ = (273 + 27) K = 300 K

For a fixed amount of gas with constant volume: P₁/T₁ = P₂/T₂
Final pressure, P₂ = P₁ × (T₂/T₁) = (6.46 atm) × (300/500) = 3.88 atm (to 3 sig. fig.)

Use
PV/T (1) = PV/T (2)
We can discount 'V' as the volume is constant.

Hence
P/T(1) = P / T(2)
P = P(1)T(2) / T(1)
P = 6.48 atm X 27 degrees/ 227 degrees
P = 0.77074 atms.