Breakdown of Ограничение по весу для личного пользования указано в таможенной декларации.
Questions & Answers about Ограничение по весу для личного пользования указано в таможенной декларации.
Because the grammatical subject is ограничение (restriction / limit), and that noun is neuter singular.
So the short passive form has to match it:
- указан = masculine singular
- указана = feminine singular
- указано = neuter singular
- указаны = plural
Since ограничение is neuter, Russian uses указано.
It comes from the verb указать (to indicate / to specify / to state), but in this sentence указано is a short passive participle used predicatively.
A natural English equivalent is:
- is indicated
- is stated
- is specified
So the structure is basically:
- Ограничение ... указано ...
- The limit ... is stated ...
This is a very common formal/written Russian pattern.