IDK these help pls

1. Which of the following is a compound?
A. O2
B. NH3
C. H2O+NaCl
D. N2

2. What is the difference between compounds and mixtures?
A. Compounds contain only one element; mixtures contain two or more elements.
B. Compounds contain two or more elements; mixtures contain only one element.
C. Compounds contain elements bonded together to form a new substance; mixtures contain elements that are combined but not bonded.
D. Compounds contain elements that are combined but not bonded; mixtures contain elements bonded together to form a new substance

3. Which of the following is formed through chemical changes?
A. Atom
B. Element
C. Compound
D. Molecule

4. Which of these describes a chemical reaction?
A. Atoms are created by elements.
B. Atoms combine to form elements.
C. Atoms of two or more elements repel each other.
D. Atoms of two or more elements bond to each other