In which of the following years did the number of families with less than 4 members in pink apartments decrease compared to last year?

We need to check for three options 

Option A: In 2021, there were 75+65=140 families in pink apartments, of which 15%, that is, 20 families, had less than 4 members. 

Looking at 2020, there were 68+62 = 130 families in pink apartments, of which 10%, that is, 13, had less than 4 members. Hence, 2021 is not our answer. 

Option B: In 2023, there were 175+175=150 families in pink apartments, of which 30%, that is, 45 families, had less than 4 members. 
Looking at 2022, there were 85 + 70 = 155 members in the pink apartment, of which 20%, that is, 21 families had less than 4 members; hence, this, too, is not our answer. 

Option C: In 2024, there were 78+62 = 140 families in pink apartments, 20 of which, that is 28 families, had less than 4 members. 
This is a decrease from 45 families in 2023

Of the given options, only 2024 had a lesser number of families with less than 4 members. 

Therefore, Option C is the correct answer.