The period of a mechanical wave is 5 seconds. what is the frequency of the wave?

10 hz
2.5 hz
0.2 hz
depends on the speed of the wave

May someone explain how to do this question?

When a neutral charge, comes into contact with a positive charge they repel each other nothing happens the neutral charge becomes negative they attract each other

How much energy must a refrigerator absorb from 225 g of water so that the temperature of the water will drop from 35°c to 5°c