Why did Mendeleeff had to leave certain blank spaces in his periodic table ? What is your explanation for this ?

Why Mendeleff has to leave certine blank spaces in his peridic table ?

Who was left the blanks in his periodic table for some undiscover elements ?

What property did Mendeleev use to classify elements in his periodic table?

What were the criteria used by Mendeleev in creating his Periodic Table ?

What are the limitations of mendeleeff's periodic table ?

How do you appreciate Mendeleeff for his great contribution in the prepartion of modern periodic table ?

Newlands proposed the law of octaves . Mendeleeff suggested eight groups for elements in his table . How do you explain these observations in terms of modern periodic classification ?

(i) Newlands proposed the law of octaves. ii) The law of octaves was not valid for elements that had atomic masses higher than calcium. iii) Newlands left blanks for new elements in his periodic table. Which statement is wrong?

Two towns A and B are connected by a regular bus service with a bus leaving in either direction every T minutes. A man cycling with a speed of 20 km h^(-1) in the direction A to B notices that a bus goes past him every 18 min in the direction of his motion, and every 6 min in the opposite direction. What is the period T of the bus service and with what speed (assumed constant) do the buses ply on the road ?