Correct Answer - Option 4 : b = a/4
A 8051 Microcontroller can perform addition, subtraction, left shifting of bits and right shifting of bits.
When there is a multiplication by nth power of 2, then there is n times left shift.
When there is a division by nth power of 2, then there is n times right shift.
The shifting operations requires the least clock cycles, hence option 4 is the correct answer.
As, there is a division of the square of 2, hence it involves just 2 times right shift.