What is the mass of 25.5 L of water assuming it is at 4 degrees Celsius?

In numbering carbon atoms in the parent chain of a hydrocarbon, why would you number from right to left, rather than left to right

Ineed to find the answer of this question because i dont understand it

The bond energy for the van der waals bond between two helium atoms is 7.9×10−4ev. assuming that the average kinetic energy of a helium atom is (3/2)kbt, at what temperature is the average kinetic energy equal to the bond energy between two helium atoms