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JEE Main levelSingle correct optionDifficulty 2 of 3mt202

The $Δ G^{\circ}$ - $T$ line for $2 Zn + O X_{2} 2 ZnO$ shows a sudden increase in slope at 1180 K (the boiling point of zinc). The reason is that

Azinc becomes less reactive towards oxygen
Bthe heat of formation changes sign at 1180 K
Czinc oxide melts at 1180 K
Dabove 1180 K zinc is a gas, so the reaction consumes more moles of gas and $Δ S^{\circ}$ becomes more negative

Answer: D

Below 1180 K only

O X_{2}

is gaseous; above it

2 Zn (g) + O X_{2} 2 ZnO (s)

removes three moles of gas.

Δ S^{\circ}

is much more negative, and the slope

- Δ S^{\circ}

increases.

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