The Wheatstone bridge is an arrangement of four resistances: $R_1, R_2, R_3, R_4$ as shown in the figure given below. The null-point condition is not given by

$R_1R_2=R_3R_4$

The correct answer is Option (4) → $R_1R_2=R_3R_4$

Condition for a balanced Meter Bridge: The bridge is said to be balanced when no current flows through the galvanometer.

Mathematical condition: $\frac{R_1}{R_2} = \frac{R_3}{R_4}$ 

Thus, $R_1R_4=R_2R_3$

Hence, Options 1, 2, and 3 all represent the correct null-point condition in different forms. However, Option 4 states:  $R_1R_2=R_3R_4$ which does not follow from the Wheatstone bridge balance condition.