A 1000-turn toroidal solenoid has a central radius of 4.2 cm and is carrying a current of 1.7 A. What is the magnitude of the magnetic field inside the solenoid at the central radius

The value is  

Explanation:

From the question we are told that

  The  number of turn is N  =  1000 turns

   The radius is  

   The current is  

Generally the magnetic field is mathematically represented as

Here is the permeability of free space with value

So  

=>  

your answer is c! hope this : )