Concept: The question tests on the basics of Mensuration.

Solution:
 

Let the dimensions of the concrete block be l, b, h for length, breadth and height respectively.

The volume of a cube = l.b.h

St(1):- Please let us know as and when you have queries in future.

The lateral faces are the four sides of the block.(You can imagine the four "walls" of a room)

Given, l h =200 and b h=200

=> l h=b h

=> l = b
However we do not know the third side to determine the value of the volume. (Insufficient)
 

St(2):- The top of the block is square and has an area of 400 square inches.

Let the dimension of the top square face be a units.

=> a^2 = 400

=> a = 20
Even though two of the dimensions are 20 each, we still do not know the third dimension needed for the volume.(Insufficient)

On combining both:-
 

l = b

l h = 200 and hence 20 * h =200 (20 is obtained as data from the second statement. You can also use b h=20)

Hence volume = lbh = 20*20*10 (Sufficient) option(C)