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Science · 2026 · 4 marks
CBSE 2026 · Region 4 · Set 1 · Q28
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of H^+ ions and OH^- ions produced by these…
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of $\displaystyle \mathrm{H}^{+}$ions and $\displaystyle \mathrm{OH}^{-}$ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution. Answer the following :
(a)
What type of indicator is used to predict how strong an acid or base is ?
(b)
Three solutions A, B and C showed pH as $\displaystyle 3$, $\displaystyle 5$ and 7. Which solution has the highest concentration of $\displaystyle \mathrm{H}^{+}$ions ?
(c)
What are strong acids and weak acids ?
OR
(c)(i)
Under what condition is rainwater called acid rain?
(ii)
In the following acids, identify weak acids : Nitric acid, hydrochloric acid, acetic acid, sulphuric acid, formic acid.
Marking-scheme solution
(a) Universal indicator
(b) \(\displaystyle \mathrm{A} /(\mathrm{pH}=3)\)
(c)
Strong acids give more \(\displaystyle \mathrm{H}^{+}\)ions in water. / Strong acids pH $\displaystyle 1$-$\displaystyle 2$
Weak acids give less \(\displaystyle \mathrm{H}^{+}\)ions in water. / Weak acids pH $\displaystyle 6$-$\displaystyle 7$
OR
(c) (i) When \(\displaystyle \mathrm{pH}<5.6\)
(ii) Weak acid: acetic acid, formic acid
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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.