Question

A gas decolourises alkaline KMnO4 solution but does not gives precipitate with AgNO3 is: a) CH4. b) C2H4. c) C2H2. d) C2H6

Answer 1

C2H4 is the gas.............

Answer 2

Answer:

The gas C2H4, ethylene or ethene reacts with potassium permanganate KMnO4 but does not give a precipitate with silver nitrate AgNO3

Solution:  

Alkenes are unsaturated hydrocarbons react more than alkanes which are saturated hydrocarbons. So upon reaction with KMnO4, an alkene oxidizes to alcohol and KMnO4 reduces to Mn2+ ions finally. This reduction of KMnO4 leads to change of color from green to brown to colorless finally.  

Ethylene C2H4 forms a permanganate ester upon reaction with potassium permanganate which further decomposes to ethylene glycol (ethane 1,2 –diol) and manganese dioxide.  

Alkenes upon reaction with silver nitrate solution do not oxidize to form any precipitate.