Waec Model Questions Vol1 2022 Chemistry Question 3

A student investigates the nature of bonding in three solid substances labelled A, B and C. The following experimental procedures are carried out: 1. A small quantity of each solid is dissolved in 50 mL of distilled water. 2. The conductivity of each solution is tested using a calibrated conductivity meter. 3. A small amount of each solid is heated over a Bunsen flame and the melting point is observed. 4. Each solid is placed in a clean porcelain crucible and heated strongly; the appearance of the residue is noted. 5. A flame test is performed by dipping a nichrome wire in the solid and introducing it into a non‑luminous Bunsen flame; the colour of the flame is recorded. The observations are recorded in the table below. | Substance | Conductivity of solution | Melting point (°C) | Residue on strong heating | Flame colour | |-----------|--------------------------|--------------------|---------------------------|--------------| | A | High | 770 | Metallic shiny | No colour | | B | Low (negligible) | 150 | White powder, no change | Yellow‑green | | C | Moderate | 660 | Brittle grey solid | No colour | Based on the above data, answer the questions that follow.