Q.Which of the following statements about hydrogen is incorrect? (NEET - 2016)
Step 1. Check (a): does not, in fact, exist "freely" as a bare ion in solution -- it is always further hydrogen-bonded to surrounding water molecules -- but the statement as commonly tested is treated as essentially true for this level (it is the accepted way of writing the hydrated proton), so it is not the targeted incorrect option.
Step 2. Check (b): dihydrogen genuinely is a good reducing agent (Section 4.3.1) -- true.
Step 3. Check (c): of hydrogen's three isotopes, protium is 99.985% abundant, deuterium about 0.015%, and tritium only a trace (~1 in 10¹⁸). Tritium is therefore the LEAST common, not the most common -- this statement is false.
Step 4. Check (d): hydrogen forms H⁺ (a cation), not H⁻ acting as a cation, in its compounds -- it never behaves as a cation in ionic salts (where it would need to appear as a metal-like species); this statement is true.
Step 5. Only option (c) is factually wrong.
(c) Hydrogen has three isotopes of which tritium is the most common.
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