Kinetin is chemically :

N⁶ -furfurylamino purine 

The correct answer is Option (3) -N⁶ -furfurylamino purine

The plant growth regulators (PGRs) are small, simple molecules of diverse chemical composition. 

They could be indole compounds (indole-3-acetic acid, IAA); adenine derivatives (N6 -furfurylamino purine, kinetin), derivatives of carotenoids (abscisic acid, ABA); terpenes (gibberellic acid, GA3 ) or gases (ethylene, C2H4 ). Plant growth regulators are variously described as plant growth substances, plant hormones or phytohormones in literature. 

Auxins like IAA and indole butyric acid (IBA) have been isolated from plants. NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins. All these auxins have been used extensively in agricultural and horticultural practices.