By what percentage will the illumination of the lamp decrease if the current drops by $20 \%$ (in $\%$)?

In a $Ag$ voltameter,$2.68 \, g$ of silver is deposited in $10 \, \min$. The heat developed in a $20 \, \Omega$ resistor during the same period will be:

If voltage across a bulb rated $220 \,V, 100 \,W$ drops by $2.5 \%$ of its rated value, then the percentage of the rated value by which the power would decrease is (in $\%$)

Two electric bulbs rated $P_1 \text{ watt}, V \text{ volts}$ and $P_2 \text{ watt}, V \text{ volts}$ are connected in parallel and $V \text{ volts}$ are applied to the combination. The total power consumed will be:

Two electric bulbs are connected one by one across a potential difference $V$. At that time,the power consumed in them is $P_1$ and $P_2$ respectively. Now,if the potential difference $V$ is applied across the series combination of these bulbs,what will be the total power consumed?

Assertion : When current through a bulb decreases by $0.5\%$,the glow of bulb decreases by $1\%$.
Reason : Glow (Power) is directly proportional to the square of current.