Which term best indicates the total number of neutrons and protons in a particular isotope of an element?     atomic number    mass number     group number    atomic mass

Mass number.

The atomic number just describes the number of protons, the group number identifies which column of a standard periodic table an element can be found in, and the atomic mass is just the mass of the atom.

Organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.