Identify the element and its position

Platinum, $\mathrm{Pt}$, has atomic number $78$.

Start from the nearest noble gas core

The noble gas preceding platinum is xenon, so we begin with: $[\mathrm{Xe}]$

Xenon accounts for $54$ electrons.

Fill the remaining electrons beyond xenon

Total electrons left after $[\mathrm{Xe}]$: $78 - 54 = 24$

After xenon, electrons enter the orbitals in the sequence involving $4f$, $5d$, and $6s$.

First fill $4f$: $4f^{14}$ Electrons used so far beyond xenon: $14$

Remaining: $24 - 14 = 10$

Expected and actual configuration

A naive filling might suggest: $[\mathrm{Xe}]\,4f^{14}5d^8 6s^2$ But platinum is one of the transition elements that shows an anomalous configuration because a more stable arrangement is obtained by promoting one $6s$ electron into the $5d$ subshell.

Hence the actual ground-state configuration is: $[\mathrm{Xe}]\,4f^{14}5d^9 6s^1$

Check the options

• A: $[\mathrm{Xe}]\,4f^{14}5d^9 6s^1$ ✅
• B: $[\mathrm{Kr}]\,4f^{14}5d^{10}$ ❌ Wrong noble gas core and incomplete representation
• C: $[\mathrm{Xe}]\,4f^{14}5d^{10}$ ❌ Missing $6s$ electron count properly for neutral Pt
• D: $[\mathrm{Xe}]\,4f^{14}5d^8 6s^2$ ❌ Aufbau expectation, but not the actual ground state

Final answer

Therefore, the electronic configuration of platinum is: $[\mathrm{Xe}]\,4f^{14}5d^9 6s^1$

So, Option A is correct.