Which of the following statements about hydrogen is /are correct? 1. Hydrogen has three isotopes of which protium is the most common. 2. Hydrogen ion (H+) exists freely in solution. 3. Dihydrogen, H2, acts as a reducing agent. Select the correct answer using the code given below.

Hydrogen naturally occurs as three isotopes: protium, deuterium, and tritium. Protium is the most abundant, making up approximately 99.985% of natural hydrogen. Statement 1 is therefore correct. Regarding statement 2, hydrogen ions (H+) cannot exist freely in solution due to their high charge density; they always combine with water molecules to form hydronium ions (H3O+) or other hydrated species [2]. Thus, statement 2 is incorrect. Statement 3 is correct because dihydrogen (H2) acts as a reducing agent, capable of reducing metal oxides to their respective metals and reacting with unsaturated organic compounds [2]. Dihydrogen's ability to donate electrons or combine with oxygen makes it a common reductant in chemical processes [2]. Consequently, only statements 1 and 3 are correct.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Activity 2.9 > p. 23
2. [2] https://www.sciencedirect.com/topics/engineering/hydrogen-isotopes
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > What you have learnt > p. 56