What does 'to be sore on Monday' mean?

[Luda from Minsk]

English Language Tests, Intermediate level

ESL/EFL Test #204 "Prepositions of Time and Date (2)", question 6

After our hiking trip, I'm going to be really sore ......... Monday morning.

(a) about
(b) in
(c) on

English Language Tests, Intermediate level

ESL/EFL Test #204 "Prepositions of Time and Date (2)", answer 6

After our hiking trip, I'm going to be really sore on Monday morning.

Correct answer: (c) on

Your answer was: incorrect
After our hiking trip, I'm going to be really sore about Monday morning.
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Could you explain what it means 'to be sore on Monday'

Luda from Minsk (Belarus)

[Kitosdad]

He is going to be feeling the effects of the walk. Sore feet and muscles.
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