Before matching case names, it helps to fix what makes a solicitor's firm different from a factory or a trading company for the purpose of the Industrial Disputes Act. A solicitor's work rests on personal skill, trust and a direct lawyer-client relationship, not on organised joint effort between capital and labour to turn out a product or service in bulk. Whichever case tests exactly this idea is the one being asked about.
Since the personal-skill reasoning applies only to the solicitor's firm case, that has to be the answer.
The correct answer is National Union of Commercial Employees v. Industrial Tribunal, Bombay.
Another route into this question is to look at where each dispute originated and what body it reached, since that often narrows down unfamiliar case names quickly.
Only the case involving employees of a solicitor's firm before an Industrial Tribunal fits both the forum and the subject matter the question is pointing to.
The correct answer is National Union of Commercial Employees v. Industrial Tribunal, Bombay.