CBSE Class 10 Science 2026 Solved Paper All Sets

Question : 17 of 20

Marks: +1, -0

In the question, two statements are given -

One labelled as Assertion (A) and other labelled as Reason (R). Write the correct answer selecting the appropriate option from (A), (B), (C) & (D) given below :

Assertion (A): Pure ethanoic acid is also known as glacial acetic acid.

Reason (R): Pure ethanoic acid often freezes during winter due to its low melting point of 290 K.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
Assertion (A) is true, but Reason (R) is false.
Assertion (A) is false, but Reason (R) is true.

Solution:

Assertion (A) : Ethanoic acid (

CH_3COOH

), commonly known as acetic acid, is indeed called "glacial acetic acid" when it is in its pure, anhydrous (water-free) form.

Reason (R) : The term "glacial" comes from the physical property of the acid. Pure ethanoic acid has a melting point of 290 K (which is approximately 17°C or 63°F).

Since 17°C is often higher than the ambient temperature in cold climates or during winter, the liquid easily solidifies.

When it freezes, it forms clear, needle-like crystals that look remarkably like glaciers or ice.

The reason we use the specific nickname "glacial" is because of the freezing behavior described in the Reason. If it had a much lower melting point (like ethanol, which melts at 159 K), it wouldn't freeze in winter and therefore wouldn't be called "glacial."

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