Water in an electric kettle becomes hot by convection. It is the process of transfer of heat by mass motion of a fluid such as water when the heated fluid is caused to move away from the source of it and carrying energy with it. Conduction is the process of transmission of heat through the material of a substance.

Explanation:
When an electric kettle is plugged in and turned on, the process of heating the water begins. The water in the kettle becomes hot primarily due to convection.

Convection:
Convection is the transfer of heat through the movement of a fluid (liquid or gas). In the case of the electric kettle, the fluid is the water. Convection occurs in three steps:

1. Heating Element:
The electric kettle contains a heating element, usually made of a metal such as stainless steel. When the kettle is turned on, an electric current passes through the heating element, causing it to heat up. The heating element is in direct contact with the water in the kettle.

2. Heat Transfer:
As the heating element heats up, it transfers heat energy to the water through conduction. Conduction is the transfer of heat through direct contact between particles or objects. The hot heating element comes into contact with the water molecules, causing them to gain energy and increase in temperature.

3. Convection Currents:
Once the water molecules near the heating element gain energy and become hot, they also become less dense. Hot water rises due to its lower density, creating convection currents. These currents cause the hot water to move upwards, while the cooler water near the top of the kettle moves downwards to replace it. This circulation of water continues as long as the heating element is active.

Other Options:
While convection is the primary mechanism for heating the water in an electric kettle, the other options mentioned in the question also play a role:

- Conduction: Conduction occurs initially when the heating element comes into direct contact with the water molecules, transferring heat energy from the element to the water.
- Radiation: Radiation is the transfer of heat through electromagnetic waves. Although the heating element may emit some radiation, it is not the primary mechanism for heating the water in the kettle.
- Motion of Molecules: The motion of water molecules, which is a result of the convection currents, contributes to the overall heating process. As the molecules move and collide, they transfer energy to each other, leading to an increase in temperature.

In conclusion, the water in an electric kettle becomes hot primarily through convection, as the heating element transfers heat energy to the water, causing convection currents to circulate and distribute the heat throughout the kettle.