When a 191 n bag of nails hangs motionless
from a single vertical strand of rope, how
much tension is exerted in the strand?
answer in units of n.

At the place where the rope meets the bag, the upward force
of the rope must be exactly the same as the downward force of
the load of nails. If the net force at that point were not zero, then
that point would be accelerating either upward or downward.  So
the upward force of the rope at that point is 191 N.

I can't tell you about the tension higher up in the rope.  If the rope
itself has any mass, then points higher up must support not only
the bag of nails but also the weight of the section of rope that is
below the point.

If the rope has no mass, then the tension is 191 N everywhere along it.

A. they hold atoms  together with a molecule.its a force that exist between molecules. hope this .