Question

Complete the sentence with the correct possible adjective
Ill va acheter ________eclairs

Answer 1

Il va acheter des éclairs

Answer 2

Bonjour

If you meant complete with the correct article, it's DES, indefinite article plural

Il va acheter des éclairs.

If you really meant a correct possible adjective, you still have to add an indefinite plural articles which is "DES" which becomes "DE" , partitive article

Il va acheter de bons éclairs.

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hope this helps ☺☺☺