Where does the cathode rays get deflected in a electric field? 

Positive plate 

The correct answer is option 1. Positive plate.

Cathode rays are streams of electrons emitted from the cathode (negative electrode) in a cathode ray tube or other vacuum tubes. These electrons are negatively charged particles.

When a cathode ray tube is placed in an electric field, such as between two charged plates, the electrons experience a force due to the electric field. According to the principles of electrostatics, the force experienced by a charged particle in an electric field is directly proportional to the charge of the particle and the strength of the electric field, and inversely proportional to the mass of the particle.

Since electrons are negatively charged, they experience a force in the direction opposite to the direction of the electric field. Therefore, in an electric field, cathode rays (electrons) are deflected towards the positively charged plate.

This deflection occurs because the negative charges (electrons) are attracted to the positive plate, leading them to move in that direction. Therefore, the cathode rays get deflected towards the positive plate when placed in an electric field.