Step 1: Understanding the Concept:
According to IUPAC, a transition element is defined as an element whose atom has a partially filled d-subshell, or which can give rise to cations with an incomplete d-subshell in its common oxidation states.
Step 2: Key Formula or Approach:
Write down the electronic configurations of the given elements in their ground state and their common oxidation states to check for partially filled d-orbitals.
Step 3: Detailed Explanation:
Let's examine the electronic configurations of the given elements:
- (A) Ni (Nickel, \(Z=28\)): \([\text{Ar}] 3d^8 4s^2\). It has a partially filled d-orbital in its ground state, so it is a transition element.
- (B) Fe (Iron, \(Z=26\)): \([\text{Ar}] 3d^6 4s^2\). It has a partially filled d-orbital in its ground state, so it is a transition element.
- (C) Ag (Silver, \(Z=47\)): \([\text{Kr}] 4d^{10} 5s^1\). While its ground state has a completely filled d-subshell, its common oxidation state of +2 (\(\text{Ag}^{2+}\)) has a \(4d^9\) configuration, which is partially filled. Thus, silver is considered a transition element.
- (D) Hg (Mercury, \(Z=80\)): \([\text{Xe}] 4f^{14} 5d^{10} 6s^2\). Mercury has a completely filled \(5d^{10}\) subshell in its ground state. Furthermore, in its common oxidation states (+1 and +2), the d-subshell remains completely filled (\(\text{Hg}^{2+}\) is \(5d^{10}\)). Because it never exhibits a partially filled d-orbital, mercury (along with zinc and cadmium from group 12) is not regarded as a true transition element.
Step 4: Final Answer:
Mercury (\(\text{Hg}\)) is not a transition element.