Sources of Energy — Science STD 10 — Question

How can you grow money plant bv vegetative propagation?

Describe any three ways in which individuals with a particular trait may increase in population.

What is scattering of light? Use this phenomenon to explain why the clear sky appears blue and the sun appears reddish at sunrise.

What is the maximum number of 60W bulbs that can be run from the mains supply of 220 volts if you do not want to overload a 5A fuse?

A convex lens of focal length 20cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?

Give reasons:
a. Platinum, gold and silver are used to make jewellery.
b. Sodium, potassium and lithium are stored under oil.
c. Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
d. Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
e. Lemon or tamarind juice are effective in cleaning tarnished copper vessels.

When a piece of limestone reacts with dilute HCl, a gas X is produced. When gas X is passed through lime water then a white precipitate Y is formed. On passing excess of gas X, the white precipitate dissolves forming a soluble compound Z.

1. What are X, Y and Z?
2. Write equations for the reactions which take place:

1. When limestone reacts with dilute HCl.
2. When gas X reacts with lime water to form white precipitate Y.
3. When excess of gas X dissolves white precipitate Y to form a soluble compound Z.

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

"Natural selection and speciation leads to evolution." Justify this statement.