Assertion & Reason Test: Acids, Bases & Salts - 2 - Class 10 MCQ

The number of replaceable hydroxyl (OH⁻) Ions in a base is called the acidity of that base. Magnesium hydroxide has 2 replaceable hydroxyl ions, therefore it's acidity is 2. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A)

The correct answer is b) Assertion (A) is true but reason (R) is false.

Explanation:

• Assertion (A): When zinc is added to dilute hydrochloric acid, hydrogen is indeed given off. This is a chemical reaction where zinc displaces hydrogen from hydrochloric acid, producing zinc chloride and hydrogen gas.

• Reason (R): The statement that "Hydrogen chloride molecules contain hydrochloric acid and hydrogen atoms" is misleading. Hydrogen chloride (HCl) is a compound consisting of hydrogen and chlorine, but it doesn't accurately explain why hydrogen gas is evolved when zinc reacts with dilute HCl.

Therefore, the assertion is true, but the reason does not correctly explain it.

The assertion is incorrect because during the electrolysis of concentrated aqueous NaCl, hydrogen gas forms at the cathode and chlorine gas at the anode.

The reason provided is accurate as ions migrate to oppositely charged electrodes.

• Assertion (A) is false
• Reason (R) is true

Thus, D is correct.

Let's evaluate the assertion and reason provided:

• Assertion (A): pH = 7 signifies pure water.

  • This statement is true. Pure water at 25°C has a neutral pH of 7, which is a result of the equal concentrations of hydrogen ions [H+][H^+][H+] and hydroxide ions [OH−][OH^-][OH−].

• Reason (R): At this pH, [H+] = [OH-] = 10^-7.

  • This statement is also true. In pure water at 25°C, the concentration of hydrogen ions [H+][H^+][H+] and hydroxide ions [OH−][OH^-][OH−] are both 10−710^{-7}10−7 M, leading to a pH of 7.

Conclusion:

Both the assertion and the reason are true, and the reason correctly explains the assertion.

Therefore, the correct answer is:

4. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

The assertion is true because weak acids have lower H⁺ concentration, leading to low conductivity. However, the reason is incorrect since strong and weak acids do not have equal H⁺ concentrations in solution.

The pH scale measures the concentration of hydrogen ions in a solution.

This indicates if the solution is acidic or basic (alkaline).

The "p" in pH stands for 'potenz' in German, meaning power.

The scale ranges from 0 (very acidic) to 14 (very alkaline).

Both the assertion and reason are true, and the reason correctly explains the assertion.

• Assertion (A): Common salt (NaCl) can absorb moisture from the air, especially when it is not pure and contains impurities such as magnesium chloride (MgCl₂), which is hygroscopic and attracts moisture.
• Reason (R): Magnesium chloride is hygroscopic, meaning it absorbs moisture. However, common salt itself does not inherently absorb moisture unless it contains such impurities, like magnesium chloride.

Thus, both the assertion and reason are true, and the reason explains why common salt absorbs moisture in general.

The primary acid present in curd is lactic acid. This acid is produced when bacteria, like Lactobacillus, ferment lactose (milk sugar) in milk, converting it into lactic acid.