Download App

Acids, Bases and Salts — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceAcids, Bases and Salts1 Mark
MCQ
For question two statements are given-one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $(a), (b), (c)$ and $(d)$ as given below:
Assertion: Phenolphthalein is an acid-base indicator.
Reason: Phenolphthalein gives different colours in acidic and basic medium
  • ✓
    Both $A$ and $R$ are true, and $R$ is correct explanation of the assertion.
  • B
    Both $A$ and $R$ are true, but $R$ is not the correct explanation of the assertion.
  • C
    $A$ is true, but $R$ is false.
  • D
    $A$ is false, but $R$ is true.
✓

Answer

Correct option: A.
Both $A$ and $R$ are true, and $R$ is correct explanation of the assertion.

Phenolphthalein is a weak organic acid and may be represented as $HPh.$
$\text{HPh}\ \ \ \ \ \ \ \ \ \ \ \rightleftharpoons\ \ \ \ \ \ \ \ \text{H}^+\ \ \ \ \ +\ \ \ \ \ \ \ \text{Ph}^-\\\text{(Colourles)}\ \ \ \ \ \ \ \ \text{(Colourles)}\ \ \ \ \ \ \ \ \text{(Pink)}$
In acidic medium, excess of $H ^{+}$ions are present and so equilibrium is towards left and hence solution is colourless. While in basic medium, $OH$ ions combine with $H ^{+}$ions to form unionised water molecules and so equilibrium is towards right and hence solution has pink colour. Therefore, phenolphthalein is an acid acid$-$base indicator.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "Assertion - Reasoning (1 Marks)" from Acids, Bases and Salts→Acids, Bases and Salts — all question types→Science STD 10 question papers→CBSE Board STD 10 question papers→CBSE Board question paper generator→

Similar questions

In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as :
Assertion : Concave mirror is best suited for use in a solar cooker.
Reason : Concave mirror converges large amount of light of the sun into the solar cooker.
→
For question two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R).$ Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below :
Assertion : The process of dissolving an acid or a base in water is highly exothermic reaction.
Reason : Water must always be added slowly to acid with constant stirring.
→
For two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below:
Assertion : A solenoid tends to expand, when a current passes through it.
Reason : Two straight parallel metallic wires carrying current in same direction attract each other.
→
In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as :
Assertion : Speciation is the development of one or more species from an existing species.
Reason : Classification is the arrangement of boat organisms into a series of groups based on physiological, biochemical or other relationships.
→
For question two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R).$ Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below : Assertion : Graphite is soft and slippery to touch.
Reason : Graphite has sheet like layered structure.
→
Assertion (A): A compass is kept near a wire carrying current gets deflected
Reason (R): Electric current is capable of producing a magnetic effect.
→
For two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below :
Assertion : Seeds are matured ovules.
Reason : The part of seed which contains stored food for baby plant is called cotyledon.
→
For two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and (d) as given below :
Assertion : Magnesium reacts with oxygen upon heating and burns brightly to form magnesium oxide.
Reason : Magnesium oxide is basic in nature.
→
For two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below :
Assertion : If pesticide is present in water bodies, then fish eating birds accumulate maximum amount of $\ce{DDT}$ in their bodies.
Reason : Pesticides are not metabolized within bodies of living organisms and get concentrated at each trophic level, leading to bioaccumulation.
→
For question two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R).$ Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below :
Assertion : Bleaching powder reacts with dilute acids to evolve chlorine.
Reason : The chlorine liberated by the action of dilute acids on bleaching powder is called available chlorine.
→