Solenoid is a structure of
a)	Nucleosomal organisation with 10nm thickness
b)	Condensed chromatin fibre with 30nm diameter
c)	Highly condensed form of chromatid with 300 nm thickness
d)	Well organised chromatid with 700 nm thickness

(b)

Solenoid Model (the supra-nucleosomal structure) explains how the nucleosomes are packed into the 200-300 Å thick nucleofilament of chromatin.

Finch and Klug (1976) found a close packing of nucleosomes to produce a nucleofilament, a fibre 100Å in diameter. The nucleofilaments (chromatin fibre) is further coiled up to a form of solenoid with a diameter of 300-350Å (30 nm). There are about six nucleosomes per turn of the solenoid coils.