Question

In the mendeleev periodic table why was ther e no mentiion of noble gases li9ke helium neon a nd argon

Answer 1

because it was not discovered till then

Answer 2

There was no mention of noble gases like helium, neon, and argon as they were not known at that time and were discovered much later. Since they are very inert gases, it was difficult to detect them with the primitive technology.