Question

A carbon compound P on heating with excess conc. H2SO4 forms another carbon compound Q which on addition of hydrogen in the presence of nickel catalyst forms a saturated carbon compound R. One molecule of R on combustion forms 2 molecules of carbon dioxide and three molecules of water. Identify P, Q, R and write chemical equations for the reactions involved.

Answer 1

it is stated that compound Q undergoes addition reaction.
thus it must be a unsaturated compound.-------1

it is turned to saturated compound in addition reaction forming compound R------2

R is combusted.thats is,it is burnt with 2molecules of CO2 and 3 molecules of H2O.
ethen is the compound which does that.
thus compound R ---ethane.
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we know that ethane is formed by addition reaction by 1.
so ,it must have been an unsaturated compound before that is Q.
it is an unsaturated compound where 2 hydrogen are added with a nickel catalyst.

            nickel catalst
C₂H₄ ---------------------C₂H₆  shows addition reaction.
                 H2

thus compound Q is ethene.

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now with 1,we know that only ethanol is reated with excess H2SO4 to give an unsaturated compound (ethene) and h20.
thus compound P is ethanol.

                          h2so4
   C2H5OH ------------------> CH2=CH2 + H2O.

-----------------------------------------------------------------------------------------------------  thus,
 compound P =ethanol
 compound Q =ethene
 compound R =ethane    
 
 hope it helps!!!!!!!!!