Allotropes are made up of ________ elements but have ________ physical properties.

Which of the following statements about a compound is incorrect ?

(a) A molecule of a compound has atoms of different elements

(b) A compound cannot be separated into its constituent elements by physical methods of separation

(c) A compound retains the physical properties of its constituent elements

(d) The ratio of atoms of different elements in a compound is fixed

A group of three elements with similar physical and chemical properties is called ------------

Allotropes are forms of the _______ element but have ________ physical properties.