Which among the following waves is used for communication by artificial satellites ?

A. Micro waves
B. Radio waves
C. A. m.
D. Infra-red waves

Why the needle of iron swims on water surface when it is kept gently ?

A. It will remain under the water, when it will displace more water than its weight
B. The density of needle is less than that of water
C. Due to surface tension
D. Due to its shape

Rain drops fall from great height Which among the following statements is true regarding it?

A. They fall with that ultimate velocity, which are different for different droplets
B. They fall with same ultimate velocity
C. Their velocity increases and they fall with different velocity on the earth
D. Their velocity increases and they fall with same velocity on the earth

Milk tastes sour when kept in the open for sometime due to the formation of __________?

A. Lactic acid
B. Citric acid
C. Acetic acid
D. Carbonic acid

Soap is prepared by boiling caustic soda with ___________?

A. Alcohol
B. Kerosene oil
C. Glycerine
D. Fats

What is the name of that system, which uses radioactivity to decide the period of materials of-pre-historic period ?

A. Radium dating
B. Uranium dating
C. Carbon dating
D. Deuterium dating

Where does the oxygen that keeps us alive come from?

A. Carbon dioxide
B. Carbonates absorbed from soil
C. Oxides of minerals
D. Water

The radio-active element used in heart pacemakers is ___________?

A. Uranium
B. Deuterium
C. Plutonium
D. Radium

Optic fibres are used in :

A. Cat scans
B. X-ray photos
C. Ultrasound scans
D. Endoscopy

The snow on the mountains does NOT melt all at once when it is heated by the sun because:

A. It becomes very hard
B. It reflects most of the heat from the sun
C. It has a low specific heat capacity
D. It has a high latent heat of fusion