This is a question from Brainzilla IQ test. It gives C as the correct answer but I cannot figure out why.
Reading left to right, top to bottom; each grid has an extra small black square. So the missing grid must have six small black squares.
Now notice that the small black squares use the same nine positions in sequence, looping back to the when they reach the bottom right.
(Numbering the positions 1-9 in natural order, we have:
one square in position 1
two squares in positions 2,3
three squares in positions 4,5,6
four squares in positions 7,8,9,1
five squares in positions 2,3,4,5,6.)
So the six squares should be in positions 7,8,9,1,2,3, which is answer C.