Peshawar Board 9th Class Past Papers Chemistry

i) Which one is a homogenous mixture?                                                       (Mark 1)

A. Smoke
B. Air
C. Fog
D. Smog
Answer:
B. Air

Q.2 i) What do you mean by mole and Avogadro’s number?         (Marks 4)

Answer:
Mole:
It is the amount (mass) of a substance that contains 6.02 x 1023 number of particles (atoms, molecules or formula units). It can also be defined as the atomic mass, molecular mass or formula mass of a substance expressed in grams.
Avogadro’s number:
6.02 x 1023 number of atoms, molecules or formula units is called Avogadro’s number. It is represented by the symbol NA. It is equivalent to one mole of the respective substance.
For example, 6.02 x 1023 particles are equal to one mole such as twelve eggs equal to one dozen.

Q.3 a) What are isotopes, Give isotopes of hydrogen.                      (Marks 4)

Answer:
Isotopes:
Isotopes are atoms of an element that have same atomic number but different atomic mass.
Isotopes of Hydrogen:
Hydrogen has three naturally occurring isotopes:

• Protium or Hydrogen
• Deuterium
• Tritium

(i) Protium or Hydrogen
Atomic number: 1
Mass number: 1
(ii) Deuterium
Atomic number: 1
Mass number: 2
(iii) Tritium
Atomic number: 1
Mass number: 3