List of top Science Questions

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

Which one of the following materials cannot be used to make a lens?

Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle

Classify the following into elements, compounds and mixtures.
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood

Which of the following will show “Tyndall effect”?

How would you confirm that a colorless liquid given to you is pure water?

Classify each of the following as a homogeneous or heterogeneous mixture.
soda water, wood, air, soil, vinegar, filtered tea.

What produces more severe burns, boiling water or steam?

Give two reasons to justify—
(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.

What is the physical state of water at— 
(a) 25°C 
(b) 0°C
(c) 100°C ?

Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.

Convert the following temperatures to the Celsius scale.
(a) 293 K
(b) 470 K

The refractive index of diamond is 2.42. What is the meaning of this statement?

You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table.

Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density.

A concave mirror produces three times magnified (enlarged) real image of object placed at 10 cm in front of it. Where is the image located?

Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Name the mirror that can give an erect and enlarged image of an object.

The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Define the principal focus of a concave mirror.

A copper wire has diameter 0.5 mm and resistivity of $1.6×10^{–8} \ Ω m$. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?

Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

If all the waste we generate is biodegradable, will this have no impact on the environment?

What are the problems caused by the non biodegradable wastes that we generate?