The electronic configurations of three elements X, Y and Z are as follows: X 2, 4
y 2, 7
z 2, 1
(a) Which two elements will combine to form an ionic compound?
(b) Which two elements will react to form a covalent compound ? Give reasons for your choice.

During the reaction of some metals with dilute hydrochloric acid, following observations were made.

i. The temperature of the reaction mixture rises when aluminium (Al) is added.

ii. The reaction of sodium metal is found to be highly explosive.

iii. Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.

Explain these observations giving suitable reasons.

State which of the following chemical reaction will take place, giving a suitable reason for each.

Zn(s)+CuSO₄(aq)→ ZnSO₄(aq) + Cu(s)

Fe(s)+ ZnSO₄(aq) → FeSO₄(aq)+Zn(s)

Zn(s)+ FeSO₄→ ZnSO₄+Fe(s)

i. Why potato chips manufacturers fill the packet of chips with nitrogen gas?

ii. A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings.

OR

i. Crystals of copper sulphate are heated in a test for some time.

(a) What is the colour of copper sulphate crystals before heating, and after heating?

(b) What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process?

ii. A metal ‘X’ when dipped in an aqueous solution of aluminium sulphate no reaction is observed whereas when it is dipped in an aqueous solution of ferrous sulphate, the pale green solution turns colourless. Identify metal ‘X’ with reason.

What is observed when a solution of sodium sulphate is added to a solution of barium chloride taken in a test tube? Write equation for the chemical reaction involved and name the type of reaction in this case.