Give two reason , why the number of elements in first period is only 2 ?

The maximum number of elements in third period is

The number of elements in the fifth period of periodic table is

Give two reasos why transition elements can form complexes.

Give the number of elements in 2^(nd)and5^(th) period in Modern Periodic Table.

Three elements X, Y and Z have atomic numbers 7, 10 and 14 respectively. (i) Identify the group number of these elements in the periodic table. (ii) Mention one unique feature each of elements Y and Z. (iii) Which of the above two elements belong to the same period ?

The first element in the periodic table is_____.

Name two elements of first period in modern periodic table.

(a) Which two criteria did Mendeleev use to classify the elements in his periodic table ? (b) State Mendeleev's periodic law. (c) Why is it not possible to give a fixed position to hydrogen in Mendeleev's periodic table ?