List of top Science Questions

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

Number of valence electrons in \(Cl^–\) ion are:

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

For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about \(\frac1{ 2000}\) times that of proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

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.

The average atomic mass of a sample of an element \(X\) is 16.2u. What are the percentages of isotopes \(^{16}X_8\) and \(^{18}X_8\) in the sample?

If bromine atom is available in the form of, say, two isotopes \(^{79}Br_{35}\) (49.7%) and \(^{81} Br_{35}\) (50.3%), calculate the average atomic mass of bromine atom.

\(Na^+\) 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.

Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and Sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

What is a balanced chemical equation? Why should chemical equations be balanced?

What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.