The greatest 4 digit number which is a perfect square, is = ?

Answer: Option C

$$\begin{array}{rl}& \text{Greatest 4 digit number}\\ & \text{ = 9999 }\\ & \text{9| }\text{9999 | 99}\\ & |81\\ & \overline{189|1899}\\ & |1701\\ & \overline{|198}\end{array}$$
Greatest four digit number is a perfect square
= 999 - 198
= 9801