NEET-UG and JEE Main Chemistry · Class 12
Detection of extra elements — NEET & JEE Questions
Detection of extra elements is a topic in Principles Related to Practical Chemistry, a Class 12 Chemistry chapter of the NEET-UG and JEE Main syllabus. TestBudy holds 12 published NEET-UG and JEE Main questions on Detection of extra elements, each with the marking scheme of the real paper.
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Detection of extra elements MCQs with solutions
10 of the 12 published questions on this topic, exactly as they appear in a test. Answers and worked solutions come with your result rather than on this page.
In Lassaigne's test, organic compounds are fused with sodium mainly to convert covalently bound extra elements into
- A. water-soluble ionic salts
- B. volatile hydrocarbons only
- C. metallic elements
- D. insoluble polymers
Why is an organic compound fused with sodium before testing for nitrogen, sulphur or halogens?
- A. It forms water-soluble ionic sodium salts of the extra elements
- B. Fusion removes carbon completely before the test
- C. Sodium acts only as an indicator for the final colour
- D. Fusion converts every heteroatom directly into its free element
During sodium fusion, nitrogen in an organic compound is commonly converted into
- A. sodium cyanide
- B. sodium nitrate
- C. ammonium chloride
- D. nitrogen dioxide
Sulfur present in an organic compound is commonly converted during sodium fusion into
- A. sodium sulfide
- B. sodium sulfate only
- C. sulfur dioxide gas only
- D. hydrogen sulfide only
A sodium extract gives a Prussian-blue colour after the appropriate iron treatment. Which extra element is indicated?
- A. Sulphur
- B. Nitrogen
- C. Chlorine
- D. Phosphorus
An organic compound containing both nitrogen and sulphur gives a blood-red colour with ferric ions after sodium fusion. Which species is responsible?
- A. Chloride ion
- B. Cyanide ion
- C. Sulphate ion (SO4^2−)
- D. Thiocyanate ion
A Lassaigne extract gives a Prussian blue colour after the appropriate iron treatment and acidification. This indicates the presence of
- A. nitrogen
- B. chlorine
- C. sulfur only
- D. phosphorus only
After preparing Lassaigne extract, acidification followed by silver nitrate gives a white precipitate soluble in ammonia. Which extra element is indicated?
- A. Chlorine
- B. Bromine
- C. Iodine
- D. Nitrogen
Before adding silver nitrate in the halogen test, why is the sodium extract boiled with nitric acid?
- A. It reduces silver ions so that metallic silver is produced
- B. It supplies chloride ions needed to form the precipitate
- C. It removes interfering cyanide and sulphide ions
- D. It converts all halides into volatile hydrogen halides
Why is the Lassaigne extract boiled with nitric acid before testing for halides when nitrogen or sulfur may also be present?
- A. To remove interfering cyanide and sulfide ions before adding silver nitrate
- B. To create more halide ions from water
- C. To precipitate sodium metal
- D. To convert silver nitrate into ammonia
Common mistakes in Detection of extra elements
Recorded against questions in this topic that are not shown above, so none of these points at an answer you can see on this page.
- Associates every coloured Lassaigne test with nitrogen.
- Uses only one test result and ignores the diagnostic halide precipitate behaviour.
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