The electronic configuration of Pt (atomic number 78) is

Platinum (Pt) has atomic number 78, so its electron configuration can be built from the xenon core (Xe, atomic number 54), leaving $$78 - 54 = 24$$ electrons to be placed beyond Xe.

Those electrons fill the subshells in the order 6s, 4f, 5d, giving an expected configuration:

(total: $$14 + 8 + 2 = 24$$ electrons)

However, platinum exhibits an exception in which one electron shifts from 6s to 5d to achieve greater stability:

(total: $$14 + 9 + 1 = 24$$ electrons)

Because the resulting near-complete d-subshell is more stable, the actual ground-state configuration of platinum is $$[Xe]4f^{14}5d^{9}6s^{1}$$.

Hence, the correct answer is Option D ($$[Xe]4f^{14}5d^{9}6s^{1}$$).