Question

The surface tension of boiling point is

Answer 1

If there is a large surface tension, it acts a bit like a sheet on the surface holding molecules in and so gives a lower evapouration rate than would otherwise be. Similarly for boiling (which is just the extreme of evapouration where the saturated vapour pressure reaches the ambient pressure) the boiling point would be raised by increased surface tension.

Answer 2

 the surface holding molecules gives a lower evapouration rate