The element that does not belong to the same period of the remaining elements (modern periodic table) is:

Solution

Chemistry ma’am · 3 steps

Write the atomic numbers first. Pd is 46, the other three are in the 70s, so Pd sits a row higher.

1. What decides period. In the modern periodic table, the period is the highest principal quantum number n in the ground-state configuration. Elements with Z from 37 to 54 are in period 5, and Z from 55 to 86 are in period 6.

   Element	Z	Valence configuration	Period	Group
   Osmium (Os)	76	[Xe]4f¹⁴5d⁶6s²	6	8
   Iridium (Ir)	77	[Xe]4f¹⁴5d⁷6s²	6	9
   Platinum (Pt)	78	[Xe]4f¹⁴5d⁹6s¹	6	10
   Palladium (Pd)	46	[Kr]4d¹⁰	5	10

2. Compare. Os, Ir and Pt are the 5d elements of period 6. Pd is a 4d element. Its outermost shell is n = 4, but it belongs to period 5 because it lies in the row that starts with Rb (5s).
3. So. Palladium is the element that is not in the same period as the others, which is option (d).

The idea to keep. Learn the noble-gas atomic numbers (2, 10, 18, 36, 54, 86). Compare Z against them and you have the period at once. A 4d element is period 5 and a 5d element is period 6.

Answer from the NTA final answer key. Solution by PrepWiser.