Answer:
3. The proton number is 15.
Explanation:
Phosphorus, P is the element with the atomic number = 15. The atomic number = Number of protons. That means:
3. The proton number is 15.
Now, the number of protons = Number of electrons = 15.
And, nucleon number = Number of protons + number of neutrons. The must abundant phosphorus atom contains 16 neutrons and nucleon number is: 15+16 = 31.
Thus, we can know which statement is true.
Answer is D. that is all of the above.
Elements are chemically joined to form compounds and every compound have unique property that helps to identify it. Compounds have different kind of properties that are unique for a particular compound that is boiling point, vapour pressure and density that provides it a unique characteristics. So the answer here will be D. that is all of the above.
D. Gravity is a dent in the fabric of space and time.
or
B. Radium is a radioactive element.
Answer : The incorrect statements are:
(A) When two nonmetals react, the compound formed is ionic.
(B) Two nonmetals can undergo an oxidation-reduction reaction.
Explanation :
Covalent compound : It is defined as the compound which is formed by the sharing of electrons between the atoms forming a compound.
The covalent compound are usually formed when two non-metals react.
The two nonmetals can not undergo an oxidation-reduction reaction.
Ionic compound : It is defined as the compound which is formed when electron gets transferred from one atom to another atom.
Ionic compound are usually formed when a metal reacts with a non-metal.
The metal-nonmetal reaction can always be assumed to be an oxidation-reduction reaction.
For example : 
In this reaction, sodium shows oxidation because the oxidation state changes from (0) to (+1) and and chlorine shows reduction because the oxidation state changes from (0) to (-1).
Hence, the incorrect statements are, (A) and (B)
A because it is the only one that a formula doesnt tell