Question

what is a solenoid? what are the three factors on which the strength of a solenoid depends

Answer 1

A solenoid is an arrangement in which a wire is wounded on a magnet closely
Three factors on which it's strength depends are
Amount of current applied
No of turns of coil
Strength​ of magnet

Answer 2

Solenoid: A closely packed insulated wire in the form of a helix such that its length is very large as compared to its diameter is called solenoid.

The three factors on which the strength of a solenoid depends are:
1). Number of turns of solenoid
2). Amount of current 
3). Quality of the material used in making the solenoid

hope it helps!!