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Science · 2026 · 3 marks
CBSE 2026 · Region 5 · Set 1 · Q27
(A) (a) Give the chemical name and formula of Plaster of Paris. (b) Write the chemical equation of its preparation. (c) Give any two uses of it.
(A)(a)
Give the chemical name and formula of Plaster of Paris.
(b)
Write the chemical equation of its preparation.
(c)
Give any two uses of it.
OR
(B)(a)
Name the acid present in ant's sting.
(b)
Give reason :
(i)
While diluting an acid, it is recommended that the acid should be added to water.
(ii)
Baking soda is used as an antacid.
Marking-scheme solution
(a)
Calcium sulphate hemihydrate
$\displaystyle \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}$
(b)
$\displaystyle \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \xrightarrow{373 \mathrm{~K}} \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+\frac{3}{2} \mathrm{H}_{2} \mathrm{O}$
(c)
Plaster of Paris is used for
making toys
to support fractured bones in right position.
(a)
Methanoic acid/ Formic acid/ HCOOH.
(b)(i)
When acid is added to water, it does not cause excessive local heating/ does not cause splash out and burns.
(ii)
Baking soda, being alkaline in nature, neutralises excess acid in stomach and provides relief.
All Acids, Bases and Salts questions2026 question paperNCERT solutions: Acids, Bases and SaltsPractice Acids, Bases and Salts →
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CBSE Class 10 Science past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.