Water is a pure substance. Which of the following is true about water? a
A chemical change is required to separate the elements present in it.

b
A physical change is required to separate the elements present in it.

c
It is made up of two compounds, each with a different set of atoms.

d
It is made up of an element and a compound.

A chemical change is required to separate the elements present in it.

Explanation:

The only true statement from the choices given is that water as a pure substance requires a chemical change to separate the elements present in it.

Water is a molecule consist of two atoms of hydrogen and one atom of oxygen.

Therefore, we see that only the first choice satisfies this problem.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

sry but any answer choices