Which one among the following is present in the nettle leaf hairs that causes burning pain?
- A.Methanoic acid
- B.Ethanoic acid
- C.Benzoic acid
- D.Acetic acid
Correct answer
Explanation
The correct answer is A, Methanoic acid. The stinging hairs on nettle leaves inject methanoic acid (formic acid, HCOOH) into the skin when touched, and this acid causes the burning pain and itching. Methanoic acid is the simplest carboxylic acid. It is also the acid in the sting of ants and bees, which is why the name formic comes from the Latin word for ant. The traditional remedy is to rub the area with the leaf of the dock plant, which often grows beside nettles, or to apply a mild base such as baking soda to neutralise the acid. Option B is wrong because ethanoic acid is the acid in vinegar and is not found in nettle hairs. Option C is wrong because benzoic acid is used as a food preservative (as sodium benzoate) and does not cause the nettle sting. Option D is wrong because acetic acid is only another name for ethanoic acid, the acid of vinegar. Exam tip: nettle, ant and bee sting = methanoic (formic) acid; vinegar = ethanoic (acetic) acid.
Practice Questions
View allThe correct order of atomic radius of Li, Na, Be and O is
- A.Na > Li > Be > O
- B.Na > Be > Li > O
- C.Be > Li > Na > O
- D.O > Be > Li > Na
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Read the full explanation →Why does the Rough Endoplasmic Reticulum look 'rough' under a microscope ?
- A.Due to the presence of ribosomes on its surface
- B.Due to the absence of ribosomes on its surface
- C.Due to the presence of lysosomes on its surface
- D.Due to the presence of mitochondria on its surface
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The endoplasmic reticulum (ER) is a network of membrane tubes and sacs inside the cell. Part of it is studded on the outside with tiny granules called ribosomes, which give it a dotted, rough look under an electron microscope; this part is the rough ER.
Read the full explanation →An aqueous solution of an acid conducts electricity. This is because
- A.It contains hydrogen ion
- B.It contains water molecules
- C.Electricity passes through it
- D.It generates electricity
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When an acid such as hydrochloric acid dissolves in water, it splits into ions: hydrogen ions (H⁺, which join water molecules as hydronium ions, H₃O⁺) and negative ions such as chloride (Cl⁻).
Read the full explanation →A wire of copper having length l and area of cross-section A is taken and a current I is flown through it. The power dissipated in the wire is P. If we take an aluminium wire having same dimensions and pass the same current through it, the power dissipated will be
- A.P
- B.< P
- C.> P
- D.2P
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The power turned into heat in a wire carrying a current I is P = I²R, and the resistance of a wire is R = ρl/A, where ρ is the resistivity of its material.
Read the full explanation →Myopia is also known as :
- A.Far-sightedness
- B.Near-sightedness
- C.Cataract
- D.Presbyopia
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A person with myopia sees nearby objects clearly but finds distant objects blurred, which is why the defect is called near-sightedness or short-sightedness.
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