What do you mean by hydrogen economy? How can it be helpful for our society?

A student wants to verify the law of conservation of mass in laboratory. He prepared 10% aqueous solution of MgSO ₄ and MgCI₂. He mixed 10 ml of both in a beaker. He weighed the flask on a balance. After some time he weighed again. There was no change in mass. Answer the following questions given below:-
(i) Was the student able to verify the law of conservation of mass? What was his mistake?
(ii) What is the value associated with it?

(i) State the Heisenberg's uncertainty principle.
(ii) Write down the significance of Heisenberg principle.
(iii) Do you think it has utility in your daily life? Justify your answer

(i) What is the basis of classification to the classification of modern periodic table?
(ii) Can you apply the concept of periodic classification to the students in a class?
(iii) What is the value associated with it?

Ionic compounds have high melting and boiling points. There is strong electrostatic force of attraction between them. Answer the following:
(i) Why ionic solids are poor conductor of electricity?
(ii) What happens to the electrical conductivity when they are dissolved in water?
(iii) What is the value associated with it?