Question

Assertion: Formaldehyde is a planar molecule.

Reason: It contains $s{p}^2$ hybridized carbon atom.

• A. Assertion and reason both are correct and reason is correct explanation of assertion.
• B. Assertion is correct statement but reason is wrong statement.
• C. Assertion and reason both are correct statements but reason is not correct explanation of assertion.
• D. Assertion is wrong statement but reason is correct statement.
• E. Assertion and reason both are wrong statements.

Answer 1

The correct option is A Assertion and reason both are correct and reason is correct explanation of assertion.

Analysing the assertion

Formaldehyde is the common name of methanal. The structure is planar as shown:


So, the assertion is correct.

Analysing the reason
According to VSEPR theory, we can use the concept of steric number (SN) to determine the hybridization of an atom.$SN=$ Number of lone pairs$+$ Number of sigma bonds


Steric Number $=0+3=3$
SN = 3corresponds to $s{p}^2$ hybridisation. In formaldehyde, carbon atom is $s{p}^2$ hybridised.

Since in formaldehyde, carbon is $s{p}^2$ hybridized and any $s{p}^2$ hybridised carbon which have three sigma bonds will show trigonal planar geometry/shape. So, the reason is correct.

Conclusion: Hence, assertion and reason both are correct and reason is the correct explanation of assertion.

So, option (A) is the correct option.