CAPF AC 2020 Q7: Science & Technology – Chemistry
Magnesium is used in
- (a) fireworks to make a bright white light
- (b) gemstones in jewellery
- (c) examination of alimentary canal of the patient
- (d) purification of water
Answer: (a) fireworks to make a bright white light
Explanation
Uses of magnesium
How to think: recall the school experiment of burning a magnesium ribbon.
It burns with a dazzling white flame.
Look for the use that needs bright white light.
Magnesium burns in air with a dazzling white light.
So it is used in fireworks, flares, flash powders and signals.
| Option | Substance actually used | Verdict |
|---|---|---|
| (a) fireworks to make a bright white light | Magnesium powder | Correct |
| (b) gemstones in jewellery | Beryllium minerals such as emerald and aquamarine | Incorrect |
| (c) examination of alimentary canal of the patient | Barium sulphate (barium meal) | Incorrect |
| (d) purification of water | Chlorine, bleaching powder and alum | Incorrect |
More on magnesium:
| Fact | Detail |
|---|---|
| Group | Alkaline earth metal (Group 2) |
| In plants | Central atom of chlorophyll |
| Alloys | Light magnesium-aluminium alloys for aircraft parts |
| Medicine | Milk of magnesia (magnesium hydroxide) is an antacid |
Answer: (a) fireworks to make a bright white light.
Why each option is right or wrong
- (a) CORRECT. Magnesium burns with a brilliant white flame, so it is used in fireworks and flares.
- (b) Incorrect. The Group 2 element linked to gemstones is beryllium (emerald, aquamarine).
- (c) Incorrect. The alimentary canal is examined with a barium meal, which is barium sulphate.
- (d) Incorrect. Water is purified with chlorine, bleaching powder or alum, not magnesium.
Key point
Magnesium burns with a dazzling white light: fireworks, flares and flash powder. Also the central atom of chlorophyll and the base of milk of magnesia.
Remember
Magnesium = bright white light in fireworks and flares.
Common mistakes
- Mixing up the uses of the Group 2 metals: beryllium, magnesium and barium.
- Choosing water purification because magnesium salts are linked to hard water.
- Forgetting the school experiment of burning magnesium ribbon with a white flame.
Exam tip
Recall the magnesium ribbon experiment: bright white flame, white ash of magnesium oxide.
Sources
- NCERT Class XI Chemistry — The s-Block Elements (uses of alkaline earth metals)
- NCERT Class X Science — Chemical Reactions and Equations (burning of magnesium ribbon)