What are fossil fuels?

Chlorine, bromine and iodine form a Dobereiner's triad. The atomic masses of chlorine and iodine are 35.5 and 126.9 respectively. Predict the atomic mass of bromine.

Is it true that when a new species is emerged, the old species will be eliminated? Why?

Which phenomenon is responsible for making the path of light visible?

List two reasons which limit the usage of solar cells for harnessing energy for domestic use.

What are scums?

Why does menstruation occur?

Mala is four-month pregnant and is worried whether the child is male or female. One day she reads an advertisement regarding a medicine which of taken for 3 months results in birth of male child. What should she do?
(a) Get the medicine and take it regularly.
(b) Visit a doctor and discuss the problem with him/her.
(c) What, in your opinion, are the chances of having a male child?

The magnification produced by a plane mirror is +1. What does it mean?

Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

In the food chain given below:
Grass\(\longrightarrow\)Grasshopper\(\longrightarrow\)Frog\(\longrightarrow\)Snake\(\longrightarrow\)Peacock
What will happen if all the frogs are removed?

What are the threats to the wildlife?

(a) What are 'magnetic field lines'? How is the direction of a magnetic field at a point determined?
 (b) List any three properties of magnetic field lines.
 (c) Draw two field lines around a bar magnet along its length on its two sides and mark the field directions on them by arrow marks.

(a) State one limitation of solar energy available from solar cells.
(b) What is the minimum wind velocity required to obtain useful energy with a windmill?
(c) Define the term 'nuclear fission'.

(i) Define pH scale. Draw a figure showing a variation of pH with the change in concentration of H⁺(aq) and OH^- (aq) ions.
(ii) Mention the range of pH of the acidic solution, basic solution, and neutral solution respectively.

Describe the process of urine formation in kidneys.

What is the difference between the chemical composition of soaps and detergents? State in brief in action of soaps in removing an oily spot from a shirt. Why are soaps not considered suitable for washing where water is hard?

The Position of three elements A,B and C in the Periodic Table is shown below:

Giving reasons, explain the following :
(a)Element A is a non-metal.
(b)Element B has a larger atomic size than element C.
(c) Element C has a Valency of 1

(a) Why did Mendel choose garden pea for his experiment? Write two reasons.
(b) List two contrasting visible characters of garden pea Mendel used for his experiment.
(c) Explain in brief how Mendel interpreted his results to show that the traits may be dominant or recessive.

Explain the refraction of light through a triangular glass prism using a labelled ray diagram.

Mention the characteristics of food chain.

Explain giving example where active involvement of local people lead to efficient management of forest.