Water should boil at at pressure — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

The normal boiling point of water is $100^\circ\text{C}$ at an external pressure of 1 atm. Boiling occurs when the vapour pressure equals the external pressure. To boil at a lower temperature ($90^\circ\text{C}$), the external pressure must be lower than 1 atm. Therefore, correct answer is C.