This is the 1305th most frequent Russian word.
серьезные
Serious.
Here, "серьезные" is used as an adjective to describe problems, emphasizing their significance and impact.
У меня возникли серьезные проблемы с проектом.
I encountered serious problems with the project.
In this sentence, "серьезное" (a singular form of the adjective "серьезные") modifies "отношение" (attitude), indicating a focused and earnest approach.
Он всегда проявляет серьезное отношение к работе.
He always exhibits a serious attitude towards work.
The word "серьезные" here describes important or critical matters requiring attention and deep discussion.