Bond dissociation enthalpies ( $kJ mo l^{- 1}$ ): $F X_{2}$ 159, $Cl X_{2}$ 243, $Br X_{2}$ 193, $I X_{2}$ 151. Consider: (i) the order is $Cl X_{2} > Br X_{2} > F X_{2} > I X_{2}$ ; (ii) the electron gain enthalpy of F is more negative than that of Cl; (iii) HF is the weakest of the hydrohalic acids in water; (iv) $F X_{2}$ has the lowest bond dissociation enthalpy among the halogens; (v) the colour of the halogens deepens from $F X_{2}$ to $I X_{2}$ . The number of correct statements is

Answer: A

(i) is true from the data: 243 > 193 > 159 > 151. (ii) is false because Cl (

- 349

) is more negative than F (

- 328 kJ mo l^{- 1}

). (iii) is true, as HF is a weak acid while HCl, HBr and HI are strong. (iv) is false because

I X_{2}

has the lowest value (151). (v) is true: pale yellow, greenish yellow, red-brown, violet. Statements (i), (iii) and (v) are correct, so the count is 3.

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Answer: A

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