Which group of elements could be placed in Mendeleev’s periodic table later on, without disturbing the original order ? Give reason.

Name two elements whose properties were predicted on the basic of their positions in Mendeleev’s periodic table.

State one example of a Dobereiner’s triad’s showing in it that the atomic mass of middle element is half-way between those of the other two.

Fill in the blanks with suitable words:

(a) The basis for modern periodic table is ______

(b) The horizontal rows in a periodic table are called _______

(c) Group 1 elements are called ______

(d) Group 17 elements are known as _________

(e) Group 18 elements are called ______

(f) According to Newland’s classification of elements, the properties of sulphar are similar to those of oxygen because sulphur is the ______ element starting from oxygen.

What is meant by (i) a group, and (ii) a period, in a periodic table ?