Answer:
Option B
Explanation:
The crystal field splitting , i.e, $\triangle _{0}$ , depends
upon the field produced by the ligand and charge on the metal ion.
So, ligands can be arranged in a series in the order of increasing field strength . This series known as spectrochemical series
eg. IΘ<BrΘ <SCNΘ <ClΘ <FΘ <OHΘ < C2O42-
$<H_{2}O $ < NCSΘ < EDTA 4- <$NH_{3}$ < en < CNΘ <CO $\because$
Among the given options , ligand ($NH_{3}$) has highest magnetic field therefore , it has maximum value for $\triangle _{0}$.
Hence option (b) is the correct answer