Concept: Canal rays (positive rays) are the positively charged ions left behind when cathode rays knock electrons off the gas atoms in a discharge tube.
Formula: $$ \text{Mass of canal ray} = \text{Mass of gas atom} - \text{Mass of lost electron} $$
Solution: - The mass of the positive ion directly depends on the mass of the gas used in the tube.
- Hydrogen (\(\text{H}_2\)) is the lightest element in the periodic table.
- When a hydrogen atom loses an electron, it becomes a single proton (\(\text{H}^+\)), which is the lightest possible canal ray particle.
- Consequently, hydrogen yields the highest \(e/m\) ratio for positive rays.
Why other options are incorrect: Helium, Neon, and Argon are all significantly heavier inert gases, so their corresponding positive ions are much more massive.
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