In the question, it is given that 1 grain placed on square 1, 2 grains on square 2, 4 grains on square 3, and 8 grains on square 4 .
The series is
1,2,4,8,16...........
As we see that in each square , the number of grains placed = 2^{n-1}.
Here n is the square number .
In the question , we need to find the number of grains placed on 12th square . And for that we have to plug n=12 that is
2^{12-1} =2^{11} = 2048
So the number of grains placed on square 12 is 2048 .
