List of top Science Questions asked in CBSE Class X

A 2000 W heater has a resistance of about 25 Ω, whereas a 100 W bulb has a resistance of 500 Ω. When 220 V is applied on these, then which of the two
Justify your answer in each case.

Study the diagram given below and answer the questions that follow :

What is dispersion of white light ? State its cause. Draw a diagram to show dispersion of a beam of white light by a glass prism.

Design an experiment to demonstrate that carbon dioxide is essential for photosynthesis. Write the observation and conclusion of the experiment.

In the experimental set-up shown above in diagram (I) atmospheric air is being passed into lime water with a syringe while in diagram (II) air is being exhaled into lime water. The time taken for the lime water to turn milky in both the test tubes is different. Give reason.

Draw the diagram of an open stomatal pore and label (I) Guard cells, and (II) Chloroplast on it. Mention two functions performed by stomata.

A few crystals of ferrous sulphate were taken in a dry boiling tube and heated. Tiny water droplets were observed in the tube after some time.

An acid 'X' present in tamarind when mixed with 'Y', produces a mixture 'Z'. 'Z' on addition to a dough when heated makes cakes soft and spongy. 'Y' is prepared from common salt and helps in faster cooking.

The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given in the following table :

I (Amperes)	0·5	1·0	2·0	3·0	3·5
V (Volts)	1·5	3·0	6·2	9·3	10·8

A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors — plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface.

Carbon is a versatile element that forms the basis of all living organisms and many of the things we use. A large variety of compounds is formed because of its tetravalency. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements.
Answer the following questions :

Pollination is an important process in sexual reproduction of plants. It is an essential process that facilitates fertilisation in plants. Pollinating agents can be wind, water, insects and birds. Several changes take place in the flower after the fertilization has taken place.

Identify the product ‘X’ obtained in the following chemical reaction:

Select a pair of natural indicator from the following :

A chemical compound used in glass, soap and paper industries is

The structural formula of Cyclohexane is

Consider the following Chemical equation: a Al₂O₃ + b HCl → c AlCl₃ + d H₂O
In order to balance this chemical equation, the values of a, b, c and d must be

Which one of the following hydrocarbons is different from the others?

Which one of the following reactions is different from the remaining three?

Select from the following a plant hormone which promotes cell division.

Part(s) of a flower which attracts insects for pollination is (are)

In an experiment to study independent inheritance of two separate traits: shape and colour of seeds, the ratio of the different combinations in F₂ progeny would be

Which of the following statement (s) is (are) true about human heart?
(a) Right atrium receives oxygenated blood from lungs through pulmonary artery.
(b) Left atrium transfers oxygenated blood to left ventricle which sends it to various parts of the body.
(c) Right atrium receives deoxygenated blood from different parts of the body through vena cava.
(d) Left atrium transfers oxygenated blood to aorta which sends it to different parts of the body.

A cross between two tall pea plants resulted in offspring having a few dwarf plants. The gene-combination of the parental plants must be

The phenomena of light involved in the formation of a rainbow in the sky are