Final answer:
The ion is identified as an aluminum ion (Al3+) with an atomic number of 13 and a valency of 3, forming AlCl3 with chlorine. Al3+ has a stable electronic configuration as it satisfies the octet rule.
Step-by-step explanation:
The ion M3+ with 2 electrons in the K shell (first shell) and 8 electrons in the L shell (second shell) can be identified as the aluminum ion (Al3+), because a neutral aluminum atom has 13 electrons with the configuration 2,8,3. After losing 3 electrons to form Al3+, it is left with an electron configuration of 2,8, resembling the nearest noble gas, neon, which indicates a stable configuration.
a) The element M is aluminum (Al).
b) The atomic number of aluminum is 13, and its valency is 3, as it forms Al3+ by losing three electrons.
c) The formula of the compound formed by aluminum with chlorine is AlCl3, following the rule that the total charge of cations must equal the total charge of anions in an ionic compound.
d) Al3+ has a more stable electronic configuration than the neutral Al because it satisfies the octet rule, having complete 8 electrons in the valence shell.