Sources of Energy — Science STD 10 — Question

Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Describe the process of respiration in the following parts of a plant:

1. Root.
2. Stem.
3. Leaves.

How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which 'can be removed by it?

Give reasons for the following:
i. Ionic compounds have higher melting and boiling points.
ii. Sodium is kept immersed in kerosene.
iii. Reaction of calcium with water is less violent.
iv. Prior to reduction the metal sulphides and carbonates must be converted into metal oxides for extracting metals.

Some of the important fossils which have been studied are those of organisms X, Y and Z. X were marine arthropods which were common between 400 to 600 million years ago. Y were the invertebrate animals (molluscs) with a flat, coiled, spiral shell which lived in the sea about 180 million years ago. Z are the extinct carnivorous or herbivorous reptiles which appeared on the earth about 250 million years ago and became extinct about 65 million years ago. What are X, Y and Z?

An object is placed at a distance of 100cm from each of the above lenses A and Calculate:

1. Image distance, and
2. Magnification, in each of the two cases.

Explain with an example, how genes control the characteristics (or traits).

The non - metal A is an important constituent of our food and most of the fuels around us. A forms two oxides B and C. The oxide B is poisonous whereas oxide C causes global warming.

1. Identify A, B and C.
2. To which group of periodic table does A belong?
3. Name another element which is placed in the same group as A.

Why is the colour of the clear sky blue?

Define 'refractive index of transparent medium'. What is its unit? Which has a higher refractive index, glass or water?