If the number of protons in one atom of an element Y is 20, then the number of electrons in its ion Y²⁺ will be: A. 20 B. 19
C. 18
D. 16

i. What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?

ii. What type of reaction is this?

iii. Write a balanced chemical equation to represent the above reaction.

OR

A brown substance ‘X’ on heating in air forms a substance ‘Y’. When hydrogen gas is passed over heated ‘Y’, it again changes back into ‘X’.

i. Name the substance ‘X’ and ‘Y’

ii. Name the type of chemical reactions occurring during both the changes.

iii. Write the chemical equations of the reactions.