In the complex PtCl4.3NH3, the number of ionizable chlorines is 1.

Explanation:

To determine the number of ionizable chlorines in the complex PtCl4.3NH3, we need to understand the structure and bonding in the complex.

1. Structure of the Complex:
The complex PtCl4.3NH3 consists of a central platinum (Pt) atom surrounded by four chloride (Cl) ligands and three ammonia (NH3) ligands. The chloride ligands are negatively charged and act as monodentate ligands, meaning they can only donate one electron pair to the central metal atom. The ammonia ligands are neutral and also act as monodentate ligands.

2. Bonding in the Complex:
In the complex, the four chloride ligands donate one electron pair each to the platinum atom, forming four Pt-Cl bonds. The ammonia ligands also donate one electron pair each to the platinum atom, forming three Pt-N bonds. These bonds are coordinate covalent bonds, where the ligands donate electron pairs to the central metal atom.

3. Ionization of Chlorines:
In the complex PtCl4.3NH3, only one of the four chloride ligands is ionizable. The ionizable chloride is the one that is not involved in any coordination bond with the platinum atom. In this case, the three ammonia ligands are bonded to the platinum atom, leaving one chloride ligand uncoordinated and ionizable.

4. Conclusion:
Based on the above analysis, the number of ionizable chlorines in the complex PtCl4.3NH3 is 1. The remaining three chloride ligands are involved in coordination bonds with the platinum atom and are not ionizable.

Therefore, the correct answer is option 'B' - 1.