How many grains of wheat will be on square 12 if there was 1 grain placed on square 1, 2 grains on square 2, 4 grains on square 3, and 8 grains on square 4?

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.