An electric immersion heater of $1.08 kW$ is immersed in water. After the water has reached a temperature of $100℃$ , how much time will be required to produce $100 g$ of steam

The heat required for producing  1 g of steam $=540\times 4.2 J=2268 J$. Energy given by immersion heater is $=1.08 kW=1080W$. Now time taken to produce 100g of steam $=(2268\times 100)/1080=210 sec$