The lowest vapor pressure is exerted by:

Explanation

Vapor pressure is determined by the strength of intermolecular forces, with weaker forces leading to higher vapor pressure. In this case, mercury has the lowest vapor pressure because it has the strongest intermolecular forces compared to water, kerosene oil, and rectified spirit. This is why mercury is the correct answer. Water has stronger intermolecular forces than kerosene oil, rectified spirit, and mercury, resulting in higher vapor pressure. Kerosene oil has weaker intermolecular forces than water and mercury, leading to higher vapor pressure. Rectified spirit falls between kerosene oil and water in terms of intermolecular forces, resulting in higher vapor pressure than mercury.