Hen the external pressure is 404 kpa, what is the vapor pressure of water at its boiling point?

Vapor pressure is 404kPa

Explanation:

Before proceeding, it is important to understand the  terms (External pressure, Vapour Pressure and boiling point) and their relationship.

Vapor Pressure is defined as pressure of a vapour from a liquid at its surface.

Atmospheric (external) pressure is the sum of pressures of all the gas components, including the vapor pressure of the liquid. This is a description of Dalton's law.

How are both pressures then related to boiling?

When vapor pressure is the same as the external pressure then a liquid is deemed to be Boiling.

This means that the Vapour pressure is also 404kPa.