Answer
A) Helium gas (He) is an element
B) Mercury (Hg) is an element
C) Sugar $(C_{12}$$H_{22}$$O_{11}$) is a compound
D) Sulfur (S) is an element
E) Lye (NaOH) is a compound
Work Step by Step
Before answering the question we must know the difference between an element and a compound; both of them are pure substances, but an element is a substance formed by atoms that have the same atomic number, therefore it must be composed of only one kind of atom ( for example: the Helium (he) ), whereas a chemical compound is a pure substance composed of at least 2 different kind of atoms. An example of a compound is the sodium hydroxide (NaOH), which is composed of sodium (Na), Hydrogen (H) and Oxygen).
A more detailed explanation can be found on page 63-64 (topic 3.1 - Classification of Matter).
