b) Two other substances that can be reacted with concentrated hydrochloric acid to form chlorine gas in the laboratory are:

• Potassium permanganate ($\text{KMnO}_4$)
• Lead(IV) oxide ($\text{PbO}_2$)

The balanced chemical equation is:

Explain how chlorine gas bleaches a red litmus paper.

Chlorine gas reacts with water (present in moist litmus paper) to form hydrochloric acid ($\text{HCl}$) and hypochlorous acid ($\text{HOCl}$). The $\text{HCl}$ makes the paper acidic (red), but the hypochlorous acid is a strong oxidizing agent that oxidizes the dye in the litmus paper, causing it to lose its color and appear bleached.

2. a) Distinguish between an element and a molecule.
An element is a pure substance consisting of only one type of atom and cannot be broken down into simpler substances by chemical means. A molecule is formed when two or more atoms are chemically bonded together, which can be atoms of the same element (e.g., $\text{O}_2$) or different elements (e.g., $\text{H}_2\text{O}$).

2. b) The diagram below represents part of the periodic table.

Element D has the highest electrical conductance. Electrical conductivity in metals is due to the presence of mobile delocalized electrons. As you move down a group, the atomic size increases, and the outermost electrons are further from the nucleus and experience less attraction, making them more mobile. D is a Group 1 metal and is below C, so its valence electron is less tightly held. Group 1 metals generally have higher conductivity than Group 2 metals in the same period.

Element E is in Group 2, Period 3, so it forms a $2+$ ion ($\text{E}^{2+}$). Element G is in Group 5, Period 2, so it forms a $3-$ ion ($\text{G}^{3-}$).
To balance the charges, 3 ions of E will combine with 2 ions of G.

The first ionization energy of D is lower than that of C. Both C and D are in Group 1. As you move down a group, the atomic radius increases, and there are more electron shells, leading to increased shielding of the valence electron from the nucleus. This reduces the effective nuclear charge experienced by the outermost electron, making it easier to remove and thus lowering the ionization energy.