Question

Which of the following CANNOT be a Bronsted base?

Select one:
a. H2O
b. NH3
c. OH-
d. CH4

Answer 1

Answer:

NH3

Explanation:

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Answer 2

Option (d) Methane  $(CH_{4} )$ cannot be a Bronsted base.

Requirement to act as a Bronsted base

• Usually a Bronsted-Lowry base should have minimum one lone pair of electrons to accept a proton,  thereby forming a new bond with that proton.
• In the gas phase, one can form $CH_3^{-}$ and $CH_5^{+}$ , which are the conjugate base and conjugate acid of $CH_4$. But these two species are very much reactive to exist in solution. So option (D) can't be a Bronsted base.
• Ammonia is the Bronsted base as it is the 'proton acceptor' - it accepts a hydrogen atom from water.
• Being the proton acceptor, water also acts as a Bronsted base.
• $OH^-$ ion accepts proton to form water molecule thereby acts as a Bronsted base.
• Thus Option (D) is the correct answer.