Answer:
0.75 atm. First option.
Explanation:
First of all, we convert the T° from C to K
21°C + 273 = 294K
-3.5°C + 273 = 269.5K
When the number of moles and the volume remain constant, we can propose this situation:
P₁ / T₁ = P₂ / T₂
The relation states a directly proportion
T° decreases → Pressure decreases
T° increases → Pressure increases
0.82 atm / 294K = P₂ / 269.5K
(0.82 atm / 294K) . 269.5K = P₂ → 0.75 atm
