Metals and Non-Metals — Science STD 10 — Question

‘‘The chromosomal number of the sexually producing parents and their offspring is the same.’’ Justify this statement.

What factors could lead to the rise of a new species?

A mixture of oxygen and ethyne is bunt for welding. Can you tell why a mixture of ethyne and air is not used?

To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.

1. In which direction-towards or away from the lens does he move the screen to focus the object?
2. How does the size of image change?
3. Approximately at what distance does he obtain the image of magnification -1?
4. How does the intensity of image change as the object moves farther and farther away from the lens?

Why government established Amrita Devi Bishnoi award?

Name the material which is the best conductor of electricity.

Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound. Write the chemical equation for its preparation. For what purpose is it used in hospitals?

What happens when a solution of sodium hydrogencarbonate is heated? Write equation of the reaction involved.