Potassium ferrocyanide (K4[Fe(CN)6]) is a coordination compound that consists of a central iron atom coordinated to six cyanide ligands. When it reacts with nitric acid (HNO3), it undergoes a redox reaction, resulting in the formation of product A.

1. Reaction between potassium ferrocyanide and nitric acid:
- The nitric acid donates a proton (H+) to the ferrocyanide ion, resulting in the formation of hydrogen cyanide (HCN) and a complex containing the iron center.
- The balanced equation for this reaction is:
K4[Fe(CN)6] + 6HNO3 -> 4KNO3 + Fe(H2O)6[Fe(CN)6] + 6HCN

2. Formation of product A:
- In the reaction between potassium ferrocyanide and nitric acid, one of the products is a complex containing the iron center, Fe(H2O)6[Fe(CN)6].
- This complex is known as a double salt, where the iron atom is coordinated to six water molecules and one ferrocyanide ion.
- The double salt is the product A formed in the reaction.

3. Reaction between product A and sodium carbonate:
- Product A, Fe(H2O)6[Fe(CN)6], further reacts with sodium carbonate (Na2CO3) to form product B.
- The balanced equation for this reaction is:
Fe(H2O)6[Fe(CN)6] + 3Na2CO3 -> 6NaOH + FeCO3 + 6H2O + 2CO2

4. Formation of product B:
- In the reaction between product A and sodium carbonate, one of the products is iron(II) carbonate (FeCO3).
- The iron atom in FeCO3 is in the +2 oxidation state and is coordinated to three carbonate ions.
- The coordination number of iron in FeCO3 is 6, as it is coordinated to six oxygen atoms (three from carbonate ions and three from water molecules).
- The total number of electrons in the t2g orbitals of the metal ion present in product B (FeCO3) is 6.
- This is because the t2g orbitals (dxy, dyz, and dzx) can accommodate a maximum of six electrons.

In conclusion, the total number of electrons in the t2g orbitals of the metal ion present in product B (FeCO3) is 6.