What information does the complete ionic equation give?

Express the following number in scientific notation. 0.026890 =

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

Ab c or d ? i’m not sure what the answer is