For whom was soldiers' mutiny the biggest blow in the February Revolution?

Correct answer: For the Tsarist government

The governing concept is the dependence of autocratic rule on the armed forces. The Tsarist government relied on soldiers to enforce orders, disperse demonstrations and protect the monarchy when civilian opposition grew. Once soldiers mutinied, refused to fire on crowds or joined the workers, the government lost its most important instrument of coercion. This sharply reduced the possibility of restoring authority and helped make the Tsar’s abdication unavoidable. The mutiny was not primarily a blow to workers’ organisations or the Petrograd Soviet, which gained strength from it. Foreign traders were not the central political institution involved. Therefore option A is correct.