Case Based Questions (MCQ)

Class 10
Chapter 2 Class 10 - Acids, Bases and Salts

## Frothing in Yamuna: The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghats and households Yamuna's pollution level is so bad that parts of it have been labelled 'dead' as there is no oxygen in it for aquatic life to survive.  googletag.cmd.push(function() { googletag.display('div-gpt-ad-1669298377854-0'); });

### d) 7

Detergents are bases . Bases have a pH greater than 7

So, the correct answer is (a) 10 - 11

• ### d) equal concentration of both hydroxide ion (OH - ) and hydronium ion (H 3 O + )

Detergent is a Base .

• And when bases are dissolved in water, they ionise to form OH - ,
• Thus, there will be high concentration of OH -

Also, Acid ionise to form H 3 O +

Since Detergent is a base, it will have low concentration of H 3 O +

So, the correct answer is (b) high concentration of hydroxide ion (OH-) and low concentration of hydronium ion (H3O+)

### 4.3 The table provides the pH value of four solutions P, Q, R and S

 Solution pH value P 2 Q 9 R 5 S 11

### d) S < P < Q < R

Acid ionise to form Hydronium Ions (H 3 O + )

• As the hydronium concentration increases, the pH decreases , causing the solution to become more acidic

Since order of pH is → 11 < 9 < 5 < 2

So, hydronium ion concentration will be of the order, S < Q < R < P

So, the correct answer is (c)

### d) decreased level of dissolved oxygen and decreased growth of algae

The phosphate ions promote the growth of algae in water

More the algae present, more the surface area of the waterbody covered and oxygen cannot penetrate into the depth of the water, it is utilized by the algae

As a result, there will be an increased growth of algae and decrease in dissolved oxygen

So, the correct answer is (a)

### d) Treating the water with washing soda

Neutralization takes place when Acid and Base react to form Salt and Water

Acid + Base → Salt + Water

Since Detergent is a base , we need an Acid

Here,

• Baking Soda is a Base
• Vinegar is an Acid
• Caustic Soda is a Base
• Wahsing Soda is a Base

Thus, we use vinegar

So, the correct answer is (b)