The substance is DNA and it would be found in the nucleus.
Answer: 
Explanation:
We know the total diameter of the cell (assumed spherical) is:

Then its total radius 
On the other hand, we know the thickness of the cell wall is
and its density is the same as water (
).
Since density is the relation between the mass
and the volume
:

The mass is:
(1)
Now if we are talking about this cell as a thin spherical shell, its volume will be:
(2)
Where 
Then:
(3)
(4)
Substituting (4) in (1):
(5)
(6)
Knowing
and
:
When a magnet is being pushed through a solenoid or when a magnet is being pulled out of a solenoid, a current would register on the galvanometer. The correct options among the three options that are given in the question are the first option and the third option. The magnet needs to be moved to generate the required current.
I am crossed between A and D but i think A is the correct one.