0How many elements known to us?
Ans: 118
Who gave the theory of triads?
Ans: Dobereiner
Who gave Octave theory?
Ans: Newlands
What is the drawback of Dobereiner traits?
Only three triads were recognised from the elements known at a time.
What is the drawback of Newlands Octave theory?
Ans: It applied to calcium, properties of newly discovered elements didn't fit into the law of Octave.
In Mendeleev periodic table how many periods and groups are there?
Ans: 7 periods and eight groups.
