Why do some elements be monoatomic?

Why do some elements form diatomic or triatomic molecules? Why do elements have different atomicities?

Why do some elements exist as molecules and some as atoms?

Why do some elements react vigorously while others are inert?

Phosphorus and sulphur show multiple valency. Why do some elements show multiple valency? Discuss with your friends and teachers.

Why do some people can't able to identify some colours ?

Why do science?

Why are some elements chemically inert?

Why do elements have different atomicities?

Why do atoms of elements try to combine and form molecules?