Is it possible to use Leibniz Criteria to find out if a positive series converges?

Question

I have to study the convergence of a positive series. I wanted to know if Leibniz criteria could be applied even though it's not an alternating series, as long as it doesn't violate the other two hypothesis.

Answer 1

No. Look at $\sum_{n=1}^\infty \frac{1}{n}$. The terms $1/n$ monotonically decrease to zero, but the series diverges.