Introduction:
To divide by 16, we need to design a circuit that can count up to 16 and then reset back to 0. This can be achieved using a counter circuit with flip-flops.

Explanation:
A counter circuit is a sequential circuit that counts the number of input pulses and generates an output based on the count. In this case, we need to count up to 16, which can be represented in binary as 10000.

Binary representation:
The binary representation of 16 is 10000, which requires 5 bits to represent. Each bit represents the state of a flip-flop in the counter circuit.

Flip-flop circuit:
A flip-flop is a basic building block of sequential circuits. It can store one bit of information and has two stable states, 0 and 1. In this case, we need 5 flip-flops to represent the 5 bits of the binary number.

Divide by 16:
To divide by 16, we need to count up to 16 and then reset back to 0. This means that the counter circuit needs to have 16 states. Since each flip-flop can represent 2 states (0 and 1), we need a total of 4 flip-flops to represent 16 states.

Example:
Let's consider a 4-bit counter circuit using flip-flops. The states of the flip-flops are represented as Q3, Q2, Q1, and Q0. When the circuit is reset, all flip-flops are set to 0. As the clock signal is applied, the circuit counts up from 0 to 15 (represented in binary as 0000 to 1111), and then resets back to 0.

Conclusion:
In order to divide by 16, we need 4 flip-flops in the counter circuit. Each flip-flop represents one bit of the binary number. This allows us to count up to 16 and then reset back to 0, effectively dividing the input by 16. Therefore, the correct answer is option B - Four flip-flops.