9701 MCQ Solution 57

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Question 57: [Inorganic > Group 7]
Which gaseous hydride most readily decomposes into its elements on contact with a hot glass rod?
A ammonia
B hydrogen chloride
C hydrogen iodide
D steam
Reference: Past Exam Paper -June 2003 Paper 1 Q17


Solution 57:
Answer: C.
A cannot be because ammonia does not decompose readily.
B cannot be because hydrogen chloride is very strong the thermal stability of hydrogen halides decrease down the group and increase up the group therefore HCl is very stable
C is the answer because again the strength or thermal stability of hydrogen halides decrease down the group iodine is below both chlorine and bromine therefore its hydrogen halide thermal stability is the weakest because hydrogen iodide bond length is long and therefore less polar than HCl therefore decompose more readily , more easily.

D cannot be answer . because HI is more weaker.

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