The correct IUPAC name of K2[PtCl4] is:

🧠 Three Things at Once

$\mathrm{K_2[PtCl_4]}$ tests three IUPAC reflexes simultaneously:

1. The complex is anionic → metal name flips to "platinate" (-ate suffix).
2. Outer cation is potassium → name as just "potassium", not "dipotassium" (modern convention drops the multiplier).
3. "Chloro" or "chlorido"? Modern IUPAC uses "chlorido".

🗺️ Construct It

Ligand block. 4 × chlorido → "tetrachlorido".

Oxidation state of Pt. $2(+1) + [x + 4(-1)] = 0 \Rightarrow x = +2$. So Pt(II).

Metal block. Anionic → "platinate(II)".

Counter-ion. Two outer K⁺ → "potassium" (no "di-").

Stitched: Potassium tetrachloridoplatinate(II) — option (3).

⚡ The Three-Filter Sweep

Running the three filters in order:

• "Tetrachloro" → reject (old convention) → kills option (1).
• "Dipotassium" → reject (multiplier on cation) → kills option (2).
• "Platinum" instead of "platinate" → reject (anionic complex needs -ate) → kills option (4).

What's left? Option (3).

⚠️ The "Platinum vs Platinate" Slip

Many students mechanically write the metal's regular name. For an anion, you must convert to the -ate form: platinum → platinate, ferrum → ferrate, cobalt → cobaltate. Forgetting this conversion is the classic single-mark-loser.

$\boxed{\text{Answer: (3) Potassium tetrachloridoplatinate(II)}}$