The fact that like charges repel each other is the underlying principle behind the working of an electroscope.

The process of transferring of charge from a charged object to the earth is called earthing.

Lightning is caused due to the accumulation of charges in clouds.

When a glass rod is rubbed with silk, it acquires a positive charge. Only statement (a) is true.

During the development of a thunderstorm, the air currents move upwards and the water droplets move downwards.

Lightning can occur between two or more clouds and between clouds and the earth.

Each fragment of the earth's crust is known as a plate.

The base plate of a lightning conductor is usually made of copper.

Washing clothes under running water is to be avoided during a thunderstorm.

Most of the earthquakes are caused by the movement of earth’s plates.

The power of an earthquake is expressed in terms of magnitude on the Richter scale.

The Indo-gangetic plane is earthquake-prone. Only option (4) is correct. 

Really destructive earthquakes have magnitudes higher than 7. Hence, option (2) is correct.

A seismograph is used to measure the intensity of an earthquake.

You will not be able to outrun the earthquake. By the time you will even reach the staircase, it will be over. Life is a strict no-no. Also, staircases are usually vulnerable structures themselves. The window pane might shatter and injure you. Very rarely will an earthquake be so strong so as to collapse an entire office block especially in this age and time. You should take shelter under a table to protect yourself from any debris/fixtures that might fall.