The unit of ionisation energy is

Lanthanoids are

The number of periods in the long form of periodic table is

Which of the following  properties  decreases along a  period?

Atomic radius is expressed in units

The law of triads was introduced by

The electronegativity scale was introduced by

Elements having incompletely filled outermost shell is known as

d- block elements are also called

The  first period has only _________ elements.