What is the essential condition for observing a rainbow?

What is the essential condition for observing rainbow ?

What are the essential conditions for formation of ammonia by Haber's process/?

What is the essential condition for addition of two vectors?

List two essential conditions for seed germination.

Write the essential condition for the following reaction: 2AgCl rarr 2Ag + Cl_2 And write one use of this reaction.

What is total internal reflection of light ? What are the two essential conditions for total internal reflection to take place ?