Impersonal expressions will always use se followed by a third-person singular verb — never plural.

Can the impersonal se be plural?

Impersonal Se vs Passive Se

However, you can differentiate passive and impersonal se sentences looking at the number—the impersonal se sentences only use the singular, never the plural.

How do you use impersonal?

Impersonal sentence example. She explored one hallway and found two guest bedrooms and an office, all decorated in the same cold, impersonal colors.