Grossir belong to the 2nd
group. Grossir is a common french verb.
Grossir is conjugated the same way that verbs that end in : -ir
Grossir is conjugated with the two auxiliaries être
Grossir verb is
direct transitive, intransitive.
verb is a direct transitive verb, so passive voice can be used.
Attention: passive voice can only be used when grossir verb is conjugated with auxiliary avoir.