(i) In solid form they are (anions & cations) closely packed, that is why they are not able to move.
(ii) In water they aquire mobility and can conduct electricity.
(iii) By this property these compounds can be applied in electroplating of all types of cells.

(i) Atomic no. of the element is the basis of classification of modern periodic table.
(ii) Students can be divided on the basis of their grasping capacity in class.
(iii) Classification can be applied in class and special attention can be paid to the students who are weak in studies.

(i) According to Heisenberg, it is not possible to measure simultaneously the position and the momentum of a microscopic particle with absolute accuracy.
(ii) It has significance for microscopic particles. After his principle both wave and particle nature were considered and quantum mechanics was developed.
(iii) It has no impact on our daily life. It applies only to the moving microscopic particles which we cannot see with our eyes.

(i) No, he could not verify the law of conservation of mass. No chemical reaction takes place between MgSO₄ and MgCl₂.
(ii) While doing the experiment one should understand the concept that reactants should react chemically. MgS04 can react with other salt.

The basic principle of hydrogen economy is the transpiration and storage of energy in the form of liquid or gaseous dihydrogen. It can be used in fuels cells for generation of electric power. It can be used as non-polluting fuel in near future.