Class 10 Science Chapter 2

              

NCERT Solutions for Class 10 Science Chapter 2 (MCQs)

Question 1.
Equal pieces of zinc granules are dropped in four test tubes. Following substances are poured in all the four test tubes. The reaction will be vigorous with

(a) CH3COOH
(b) HCl
(c) sodium bicarbonate solution
(d) lemon juice

Answer:-(b) Strong adds like HCl react vigorously with active metals like Zn and form metal salt and evolve H2 gas.

Question 2.
Which of the following statements shows the property of an acid?
(a) It turns blue litmus to red
(b) It is sour in taste
(c) It has no effect on red litmus
(d) All of the above

Answer:-(d) An acid turns blue litmus red. Thus, it has no effect on red litmus and acids are sour in taste.

Question 3.
A drop of a liquid sample was put on the pH paper. It was observed that the colour of the pH paper turned blue. The liquid sample is 
(a) lemon juice
(b) sodium bicarbonate solution
(c) distilled water
(d) hydrochloric acid
Answer:
(b) The liquid sample is of sodium bicarbonate (NaHC3) solution. It is a basic solution. And we know that a basic solution turns pH paper blue.

Question 4.
Two solutions X and Y were found to have pH value of 4 and 10 respectively. The inference that can be drawn is 
(a) X is a base and Y is an acid
(b) Both X and Y are acidic solutions
(c) X is an acid and Yis a base
(d) Both X and Y are bases
Answer:
(c) Any solution having pH > 7 will be a base while the solution having pH < 7 will surely be an acid. Hence, it can be concluded that X is an acid (pH=4, i.e. < 7) and Yis a base (pH =10, i.e. > 7).

Question 5.
A student was asked to collect apparatus from lab store, for doing experiment of pH of given sample. Identify the article which he is not supposed to pick.
(a) pH paper
(b) Dropper
(c) Litmus paper
(d) Petri dish
Answer:
(d) Petri dish is not required for doing experiment of pH.

Question 6.
Which one of the following would you need to identify the gas that evolve when you heat NaOH solution with zinc metal?
(a) Red litmus solution
(b) Blue litmus solution
(c) A burning splinter / matchstick
(d) Lime water
Answer:
(c) When a base like NaOH is treated with any active metal like Zn, it produces H2 gas. And the presence of the hydrogen gas can be tested by bringing a burning splinter/ matchstick near the gas produced. The gas will burn with a pop sound confirming the presence of hydrogen gas.

Question 7.
A solution has pH value of 5. On adding 10 mL of NaCl to it, what will be the pH of the new solution?
(a) More than 5
(b) Less than 5
(c) Only seven
(d) No change in pH
Answer:
(d) As NaCl is a neutral solution due to its complete ionization in H2O and has pH = 7. Thus, it will not affect the pH of the solution. Hence, the pH of the solution will remain unaffected.

Question 8.
A salt is dissolved in water. The pH of this salt solution was found to be 7 by measuring the pH with a universal indicator paper. The salt is most likely to be
(a) Na2CO3
(b) KCl
(c) NH4Cl
(d) CH3COONa

Answer:
(b) Salts which are completely ionisable in water are said to be neutral salts and their pH is equal to 7.Among the given salts, only KCl is completely ionisable in the following manner: KCl (aq) → K+ + Cl

Hence, the pH of KCl will be 7.

Question 9.
A student performed an experiment using zinc granules and . sodium carbonate with sodium hydroxide and hydrochloric acid under different
conditions as shown below.

In which set up, no gas is evolved?
(a) I
(b) II
(c) III
(d) IV

Answer:
(d) Gas will not evolve in the case of IV set up as NaOH does not react with sodium carbonate.

Question 10.
Four set ups as given below are arranged to identify the gas evolved when dilute hydrochloric acid was added to zinc granules. Which is the most appropriate set up?

(a) I
(b) II
(c) IV
(d) III

Answer:
(c) The gas evolved can be tested as shown in IV set up because to evolve H2 gas delivery tube, should not dip in the acid.

Question 11.
Four students I, II, III and IV were asked to examine the changes for blue and red litmus paper strips with dil. HCl (Solution A) and dil. NaOH (Solutions). The following observations were reported by the 4 students. The sign …………. indicates no colour change.

	Litmus	A	B	Litmus	A	B
I	Blue	—	red	Blue	red	—
II	Red	—	blue	Red	—	blue
III	Blue	red	red	Blue	blue	blue
IV	Red	blue	blue	Red	red	red

The correct observation would be of student
(a) I
(b) II
(c) III
(d) IV

Answer:
(c) The correct observation is taken by student III because HCl (solution A) is an acid which turns blue litmus red and dil. NaOH (solution B) is a base which turns red litmus blue.

Question 12.
A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish orange. Which of the following would change the colour of this pH paper to greenish blue?
(a) Lemon juice
(b) Vinegar
(c) Common salt
(d) An antacid

Answer:
(d) As pH paper turns greenish blue for weakly basic compound and antacids contain weak base like Mg(OH)2. So, an antacid would change the colour of this pH paper to greenish blue. Other options (a) and (b) contain acids and option (c) is a neutral salt.

       

                                                     https://amzn.to/2ZYQUbX

                                            

✌✌✌✌✌✌✌✌✌✌✌✌✌✌✌✌✌✌✌✌