Final answer:
The width of the narrow groove (minor groove) in B-DNA is not explicitly mentioned in the reference, but it is proportionally smaller than the major groove within the 2 nm diameter of the DNA double helix.
Step-by-step explanation:
The B-DNA form is the most common double helical structure found in living cells and it has a distinctive width for its grooves. The narrow groove, known as the minor groove, is where the sugar-phosphate backbones are close together. Detailed analysis of DNA's diffraction patterns reveals that the major groove is where these backbones are far apart, providing larger access to proteins. This asymmetrical spacing is crucial for the binding of proteins, which can then regulate processes such as replication and transcription. The specific width of the narrow groove is not directly mentioned in the reference information provided. However, considering that the diameter of the DNA double helix is 2 nm and features major and minor grooves, where the space for the minor groove would be proportionally less than that of the major groove, but exact measurements would typically be gleaned from empirical data or advanced textbooks specific to molecular biology.