Final answer:
This is an argument. The student presents a logical sequence of statements to support the claim that a grain of sand has mass.
Step-by-step explanation:
This is an argument. An argument is a logical sequence of statements that aims to persuade or convince someone of a particular position or belief. In this case, the student is presenting a logical argument to support the claim that a grain of sand has mass. They start by stating that every single atom in a grain of sand has mass, which is a fact. They then explain that since mass is an additive property, it must be the case that a grain of sand has mass. This is a valid and coherent argument, as it is supported by factual information and logical reasoning.