(1) atomic number is the correct answer.

An atom’s atomic number is the number of protons found in an atom.  It uniquely identifies a chemical element. 
The other choices cannot identify an element because these properties can be shared by other elements, so they are not unique properties.

(2) lithium atom is the correct answer.

The atomic number tells you the number of electrons; in this case, lithium has three electrons, so its first orbital contains 2 electrons and its

second orbital is only partially filled because it only contains 1 electron.

(3) +7 is the correct answer.

The atomic number of nitrogen is 7, so its nucleus is composed of 7 protons and seven neutrons.  (7 electrons surround the nucleus).  Because each proton carries a positive charge and neutrons are neutral, the nucleus carries a charge of +7.

(2) atomic mass is the correct answer.

The atomic mass depends on the average of the isotopes of the element; for this reason, it is not a whole number.  The atomic number is

constant and the same for all isotopes, so it is not affected by the relative abundance.

(2) 12 atomic mass units is the correct answer.

An atomic mass unit (Dalton) is the approximate mass of a hydrogen atom, a proton, or a neutron.  Electrons have a very small mass relative

to protons and neutrons.

(4) 310 g/mol is the correct answer.

In order to calculate gram formula mass, you simply need to count the number of atoms in the compound and refer to the molar masses on your periodic table.

In this compound there are 3 Ca atoms (3 x 40), 2 P atoms (2 x 31), and 8 O atoms (8x16). 
120 + 62 + 128 = 310 g/mol.

(2) neon, only

Although argon and neon are in the same column of the periodic table, they have different electron configurations.

The configuration of argon is : 1s^2 2s^2 2p^6 3s^2 3p^6

And the configuration of neon is: 1s^2 2s^2 2p^6

This question tests your knowledge in the difference between electron configuration and valence electrons (in this case argon and neon are the same).  Remember that the ions formed by NaF are more similar to neon (and located between Na and F on the periodic table) than they are to argon.

2-7-4-1

2-7-5

You can see this shortened version comes from the longer normal electron configuration for silicon which is:1s2 2s2 2p6 3s2 3p2

This can also be written as 2-8-4; however, when the silicon atom is excited, an electron travels from the 2nd to the third shell or from the 2nd to the fourth shell.