BECE Science 2010 Paper

Concept:A suitable thermometer liquid must remain in the liquid state over the required temperature range and expand uniformly with temperature.Explanation:The thermometer must measure about $150^\circ\mathrm{C}$.Water boils at $100^\circ\mathrm{C}$, so it cannot measure $150^\circ\mathrm{C}$ because it would turn into vapour.Alcohol boils at about $78^\circ\mathrm{C}$, so it also becomes vapour well before $150^\circ\mathrm{C}$.Mercury stays liquid from $-39^\circ\mathrm{C}$ to $357^\circ\mathrm{C}$.Therefore, $150^\circ\mathrm{C}$ lies safely within the liquid range of mercury.Mercury also expands uniformly with temperature and does not stick to the glass capillary, giving accurate readings.Turpentine is not as suitable as mercury, as its boiling point is close to the required temperature range.Hence, mercury is the best choice among the given liquids.Answer:B. mercury.