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Which of the following react with KMnO4 but does not react with AgNO3?
A. C2H6
B. CH4
C. C2H4
D. C2H2

Answer
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Hint: KMnO4 and AgNO3 are strong oxidising agents and alkanes are saturated hydrocarbons in a saturated hydrocarbon carbons valency is completely fulfilled sigma bonds and maximum number of Hydrogen is attached with it. Thus, saturated hydrocarbons are highly stable and to break the C-H bond large amounts of energy is required.

Complete Step by Step Answer:
As we can see that,
- C2H6 is the formula of ethane
- CH4 is the formula of methane
- C2H4 is the formula of ethene
- C2H2 is the formula of acetylene

Now since methane and ethane are saturated hydrocarbons, they will not react with either KMnO4 or AgNO3.
When ethene is mixed with KMnO4 diol is formed.
CH2=CH2 KMnO4 → CH2(OH)-CH2(OH)
But, when ethene is mixed with AgNO3
CH2=CH2 AgNO3 →No reaction
Now acetylene when mixed with KMnO4 and AgNO3. It gives a reaction with both

When it reacts with KMnO4 the product will be acid-
CH≡CH KMnO4 /H2O → O=CH-CH=O [O] → HOOC-COOH
At first Ethane 1,2-dial is formed which on further oxidation gives oxalic acid.
When acetylene reacts with ammoniacal AgNO3 the product formed will be-
CH≡CH AgNO3(NH3) → AgC≡CAg + 2NH4NO3 + 2NH3

The product formed in this reaction is disilver acetylide. So, we can see that alkanes that is methane and ethane does not react with either KMnO4 or AgNO3 and acetylene reacts with both KMnO4 and AgNO3 only ethene is the one that react with KMnO4 but does not react with AgNO3. So, the correct answer is ethene.
Thus, Option (C) is correct

Note: As we can see that ethene and acetylene both react with KMnO4 during the reaction it decolourises its pink colour. KMnO4 is a very good oxidising agent, with exhaustive oxidation it proceeds in the formation of carboxylic acid. It oxidises aldehydes and ketones into carboxylic acid.