List of top Science Questions asked in CBSE Class IX

Complete the following table.

Atomic Number	Mass Number	Number of Neutrons	Number of Protons	Number of Electrons	Number of the Atomic Species
9	-	10	-	-	-
16	32	-	-	-	Sulphur
-	24	-	12	-	-
-	2	-	1	-	-
-	1	0	1	0	-

Which one of the following is a correct electronic configuration of sodium?

Isotopes of an element have

Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

Composition of the nuclei of two atomic species X and Y are given as under 

	X	Y
Protons	6	6
Neutrons	6	6

Give the mass numbers of X and Y. What is the relation between the two species?

If Z=3, what would be the valency of the element? Also, name the element.

\(Na^+\) has completely filled K and L shells. Explain

Compare the properties of electrons, protons and neutrons.

Explain with examples
(i) Atomic number,
(ii) Mass number,
(iii) Isotopes
(iv) Isobars.
Give any two uses of isotopes.

Describe Bohr’s model of the atom.

Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.

Compare all the proposed models of an atom given in this chapter.

What are the limitations of Rutherford’s model of the atom?

What are the limitations of J.J. Thomson’s model of the atom?

Calculate the molar mass of the following substances.
(a) Ethyne, \(C_2H_2\)
(b) Sulphur molecule, \(S_8\)
(c) Phosphorus molecule, \(P_4\) (Atomic mass of phosphorus= 31)
(d) Hydrochloric acid, \(HCl\)
(e) Nitric acid, \(NO_3\)

Write the chemical formulae of the following.
(a)Magnesium chloride
(b)Calcium oxide
(c)Copper nitrate
(d)Aluminium chloride
(e)Calcium carbonate

What are polyatomic ions? Give examples.

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 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”?