The gibberellin involved in flowering is

The correct option is GA9.

Gibberellins (GAs) are a large family of tetracyclic diterpenoid plant hormones that regulate various developmental processes, including seed germination, stem elongation, leaf expansion, pollen maturation, and flowering.

While gibberellins like ${\text{GA}}_1$ and ${\text{GA}}_3$ are well-known for promoting stem elongation and vegetative growth, research has shown that specific gibberellins play distinct roles in reproductive development. Specifically, in many plants (including certain long-day plants and woody species), non-13-hydroxylated gibberellins like ${\text{GA}}_9$ (or its immediate metabolites) are highly active and specifically involved in the induction of flowering and floral development.