The lithium atom is represented by the symbol [tex]${ }_3{ }^7\text{Li}$[/tex], where 3 is its proton number (atomic number) and 7 is its nucleon number (mass number, which is the sum of protons and neutrons). Since the nucleon number is 7 and the proton number is 3, the lithium atom has 4 neutrons (7 - 3 = 4).
When lithium forms an ion in lithium chloride (LiCl), it typically loses one electron to achieve a stable electron configuration. The loss of this electron turns the lithium atom into a positively charged ion, specifically a +1 ion.
1. The nucleon number (7), which is the sum of protons and neutrons, remains unchanged because it only depends on the number of protons and neutrons.
2. The proton number (3) also remains unchanged as it identifies the element and does not change during the ionization process.
Hence, the lithium ion in lithium chloride maintains its proton number of 3 and nucleon number of 7 but becomes positively charged due to the loss of an electron.
Given the options:
- [tex]\( \mathbf{A\ _2{ }^6 Li^{-}} \)[/tex]: Incorrect, as this does not match the proton number or the nucleon number of lithium.
- [tex]\( \mathbf{B\ _3{ }^6 Li^{+}} \)[/tex]: Incorrect, as the nucleon number does not decrease during ionization.
- [tex]\( \mathbf{C\ _3{ }^7 Li^{+}} \)[/tex]: Correct, as it correctly maintains the nucleon number of 7, the proton number of 3, and indicates the loss of one electron with the [tex]\( + \)[/tex] charge.
- [tex]\( \mathbf{D\ _3{ }^7 Li^{-}} \)[/tex]: Incorrect, as lithium does not form a negative ion in lithium chloride.
Therefore, the correct symbol for the lithium ion in lithium chloride is:
[tex]\(\boxed{\mathbf{C\ _3{ }^7 Li^{+}}}\)[/tex]
