Select the correct option regarding the following two statements labelled Assertion (A) and Reason (R). Assertion (A): Unsaturated hydrocarbons give a yellow flame with black smoke. Reason (R): They burn completely when oxygen is insufficient.
A is true, but R is false.
Unsaturated hydrocarbons (alkenes and alkynes) have a higher percentage of carbon than the alkane of the same size, so they need more oxygen for complete combustion.
In ordinary air, oxygen supply is limited relative to their carbon content, so combustion is incomplete. Unburnt carbon particles (soot) glow yellow-orange in the flame and escape as black smoke, giving the characteristic yellow sooty flame. So Assertion (A) is true.
The Reason states they burn completely when oxygen is insufficient. This is the opposite of the truth: complete combustion requires sufficient oxygen; with insufficient oxygen the burning is incomplete. So Reason (R) is false.
Hence, A is true but R is false.
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Important Questions from Hydrocarbons
- Which structural feature contributes to the high reactivity of unsaturated organic compounds?
- Unsaturated hydrocarbons usually produce:
- Which property of carbon allows it to form a large number of compounds by bonding with itself and other elements?
- Which type of bond is present between carbon atoms in saturated hydrocarbons?
- Power Alcohol is a mixture of ______ and ethyl alcohol.
