The mass number is the total number of nucleons (protons and neutrons) in an atom's nucleus. An atom that undergoes alpha decay will lose a helium nucleus. This decreases its mass number by four. All other forms of radioactive decay listed alter the atomic number of the atom, but not the mass number.

Beta emission involves the conversion of a neutron to a proton and an electron, but only expels the electron.

Electron capture involves the conversion of a proton and an electron into a neutron.

Positron emission involves the conversion of a proton to a neutron and a "positron," or positively charged electron.

The half-life is the time it takes to reduce a sample by one-half of the original quantity. The substance would have to go through four half-life cycles to go from 64 atoms to 4 atoms.

If the total time for four cycles is 6 hours, then the half life is:

The highest energy electrons are those that are in the orbitals most removed from "s," in the order of .

As you add electron shells (n = 1 to n =2 to n = 3 and so on), you add one more of these orbitals. The result is that hydrogen only has an "s" orbital because it has n = 1, but oxygen has "s" and "p" because it has n = 2.

In order to find the hybridization of an atom, simply count the number of sigma bonds and lone electron pairs around the atom. The s subshell is filled first, followed by the three p subshells.

Carbon as a reactant (methane) has four hydrogens around it, giving it four bonds. As a result, it displays sp³ hybridization.

As a product (carbon dioxide), carbon is attached to two oxygen atoms. These two sigma bonds give the carbon sp hybridization.

The f orbital is expressed in the lanthanides and the actinides. These groups contain fourteen elements in each row. Since each suborbital can contain two electrons, the correct answer is fourteen divided by two, or seven.

The trend for suborbitals is determined by the l quantum number. The number of possible values for l determine the number of subshells.

An  shell contains 3s, 3d, and 3p subshells. Any s shell can hold up to two electrons, any p shell can hold six electrons, and any d shell can hold ten electrons.

This question is best solved by using quantum numbers. We are given the principle quantum number. Using this, we can work down to determine how many electrons can fit in this shell. The rules for quantum numbers are given below.

If the principle quantum number is three, then the next quantum number can be zero, one, or two. These correspond to the s, p, and d subshells, respectively.

After that, the next quantum number describes the orbitals within the subshells. Each orbital can carry two electrons, according to the final quantum number.

In total, there are eighteen electrons allowed in all subshells of the third energy level.

Hund's rule states that every orbital in a subshell must be half-filled (occupied by one electron) before a second electron is added to any of them, thus, Hund's rule is the correct answer. The Pauli exclusion principle states that no two electrons may have the same four quantum numbers, and Heisenberg's uncertainty principle says that we cannot simultaneously know the position and momentum of a subatomic particle. Newton's laws and VSEPR rules have nothing to do with quantum mechanics.

Bond distance is related to the type of bond between the two atoms. The more bonds between two atoms, the shorter the distance. In other words, a triple bond is shorter than a double bond, and a double bond is shorter than a single bond. Ethyne is the only option that has a triple bond between the carbons, so it has the shortest bond distance.

Each period (row) of the periodic table corresponds to a principle quantum number, or electron energy shell. An electron is added for each element as one moves across the period. The first two electrons (groups 1 and 2) are placed in the s subshell. The next six electrons (groups 13 through 18) are placed in the p subshell.

Chlorine has an atomic number of 17, meaning that it will have a total of 17 electrons distributed through these shells and subshells. Start at the 1s subshell and work upward. Note that there is no 1p subshell.

Chlorine: 1s²2s²2p⁶3s²3p⁵

Another way of writing electron configuration for an element is to first write the noble gas that comes immediately before that element in brackets, and then write the rest of the notation. For example, the bracket notation for chlorine would be: [Ne]3s²3p⁵. 

Potassium (K) is orignially in the electron configuration of [Ar]4s¹. To obtain a +1 charge it loses an electron, resulting in a configuration of [Ar].