"We do not need this soap."

Translation: Nie potrzebujemy tego mydła.

[DenitsaZarkova]

Why 'mydełko' is not correct?

[luless]

Nie potrzebujemy tego mydełka - should be accepted.

[Annieolivi]

Why is 'ta' mydła incorrect? Why is it 'tego'?

[alik1989]

Potrzebować requires the genitive case, which is "tej" for feminine nouns and "tego" for masculine and neuter nouns. "Mydło" is neuter.

https://en.wiktionary.org/wiki/ten#Declension_3

[diego808944]

Is "Mydlo" correct as genitive? I apologize: I'am aware that I have written "mydlo" in a wrong way, but I do not have the special Polish character on my keyboard.

[Jellei]

No, the Genitive form of "mydło" is "mydła", as it can be seen here: https://en.wiktionary.org/wiki/myd%C5%82o#Declension_2

[Darth_Elven]

To mydlo nam nie potrzebno?

[Jellei]

To mydło (jest) nam niepotrzebne.

[Yola448704]

We do not need this soap - To mydło nie jest nam potrzebne