This is the 8573rd most frequent Russian word.
обязательны
"Обязательны" means "mandatory" or "required."
In this sentence, "обязательны" conveys the sense of something being mandatory or required.
Эти правила обязательны для всех.
These rules are mandatory for everyone.
Here, "обязательны" is used to express a requirement or necessity.
Чтобы поступить в университет, обязательны хорошие оценки.
To enter university, good grades are required.
In this example, "обязательны" is used in an interrogative form to question whether something is obligatory.