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Which one of the following statements is incorrect ? (1) Atomic hydrogen is produced when H2 molecules at a high temperature are irradiated with UV radiation. (2) At around 2000 K, the dissociation of dihydrogen into its atoms is nearly 8.1%. (3) Bond dissociation enthalpy of H2 is highest among diatomic gaseous molecules which contain a single bond. (4) Dihydrogen is produced on reacting zinc with HCl as well as NaOH(aq).

1. Atomic hydrogen is produced when H2 molecules at a high temperature are irradiated with UV radiation.
2. At around 2000 K, the dissociation of dihydrogen into its atoms is nearly 8.1%.
3. Bond dissociation enthalpy of H2 is highest among diatomic gaseous molecules which contain a single bond.
4. Dihydrogen is produced on reacting zinc with HCl as well as NaOH(aq).

Correct answer: At around 2000 K, the dissociation of dihydrogen into its atoms is nearly 8.1%.

Solution

The incorrect statement is (2): at about 2000 K the degree of dissociation of dihydrogen into atoms is only ~0.081%, not 8.1%. The other three statements (UV/arc gives atomic H; H2 has the highest single-bond dissociation enthalpy; Zn reacts with both HCl and NaOH to give H2) are all correct.

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