Gravitation — Science STD 9 — Question

Ozone hole over Antarctica appears during:

1. Spring.
2. Summer.
3. Autumn.
4. Winter.

Chlorofluorocarbons have been in use for:

1. Aerosol propellants.
2. Formation of foam.
3. Refrigerators.
4. All the above.

Which one of the following is not a metalloid?

1. Boron.
2. Silicon.
3. Gallium.
4. Germanium.

J.J. Thomson discovered _________ at the end of 19th century.

A key of mechanical piano is first struck gently and then struck again but much harder this time. In the second case:

1. Sound will be louder but pitch will not be different.
2. Sound will be louder and the pitch will also be higher.
3. Sound will be luder but pitch will be lower.
4. Both loudness and pitch will remain unaffected.

Balanced Force:

AIDS is due to:

1. Reduction to number of helper T-cells.
2. Reduction in number of killer T-cells.
3. Autoimmunity.
4. Non-production.

Cartilage is produced by:

Haversian canals are present in:

Choose the incorrectly matched pair from the options given below.