See explanation below.
Work Step by Step
1 Concept : Like metal atoms, large numbers of nonmetal and metalloid atoms can form bands of Molecular Orbitals. Band theory explains differences in electrical conductivity and the effect of temperature among these three classes of substances in terms of the presence of an energy gap between their valence and conduction bands. Following are the three types of elements on this basis : Conductors : The valence and conduction bands of a conductor have no energy gap between them, so electrons flow when a tiny electrical potential difference is applied. When the temperature is raised, greater random motion of the atoms hinders electron movement: conductivity decreases when a metal is heated. Semiconductors : In a semiconductor, a small energy gap exists between the valence and conduction bands. Thermally excited electrons can cross the gap, allowing a small current to flow: in contrast to a conductor, conductivity increases when a semiconductor is heated. Insulators : In an insulator, a large energy gap exists between the bands: no current is observed even when the substance is heated. 2 (a) Phosphorous : Phosphorous is a GROUP 5A element of the modern Periodic Table. Hence, it falls into the category of Non-metals. Non-metals are poor conductors of Electricity. Ans :Insulator. 3 (b) Mercury : Mercury is present in group 2B of the modern periodic table. It's block is D-block. D-block elements are called 'Transition metals'. As all the metals are good conductors of electricity, Mercury can be rightly classified as a conductor. Ans : Conductor. 4 (c) Germanium : Germanium is a metalloid. Metalloids have properties common to both Metals and Non-metals, it can be rightly classified as a Semi-conductor. Ans : Semi-Conductor