True, acid rain is a secondary pollutant
Examples of a secondary pollutant include ozone, which is formed when hydrocarbons and nitrogen oxides combine in the presence of sunlight, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water.
The quantum mechanics theory
Answer:
The critical stress required for the propagation of an initial crack
= 21.84 M pa
Explanation:
Given data
Modulus of elasticity E = 225 ×

Specific surface energy for magnesium oxide is
= 1 
Crack length (a) = 0.3 mm = 0.0003 m
Critical stress is given by
=
-------- (1)
⇒ 2 E
= 2 × 225 ×
× 1 = 450 ×
⇒
a = 3.14 × 0.0003 = 0.000942
⇒ Put these values in equation 1 we get
⇒
=
⇒
= 4.77 × 
⇒
= 2.184 ×

⇒
= 21.84 
⇒
= 21.84 M pa
This is the critical stress required for the propagation of an initial crack.