Learn Farsi: این دسته یکباره بی‌حرکت می‌ایستند و پراکنده می‌شوند. - This group all at once stands motionless and disperses.

In Farsi, collective nouns—words that represent a group of living things, like دسته (group/flock), مردم (people), or خانواده (family)—usually take a plural verb. Even though the word itself is grammatically singular, the verb agrees with the plural meaning of the people or animals inside that group.

How is the word یکباره ("all at once") formed?

It is built from یک (one), بار (time/instance), and the suffix ـه which turns it into an adverb. Literally, it means "in one time" or "suddenly". You will often see بار in other frequency words like دوباره (again/twice).

Does the prefix بی‌ in بی‌حرکت work like "un-" or "-less" in English?

Yes, بی‌ means "without". Attached to the noun حرکت (movement), it creates the word بی‌حرکت (motionless / without movement). You can use this prefix with many nouns, such as بی‌کار (unemployed) or بی‌پول (penniless).

Why is پراکنده می‌شوند used for "disperses" instead of a single verb?

Farsi relies heavily on compound verbs. پراکنده is an adjective meaning "scattered" or "dispersed", and شدن (conjugated here as می‌شوند) means "to become". So instead of a single verb for "disperse", Farsi literally says "they become scattered".