Explanation:

The lattice energy is the energy released when gaseous ions combine to form a solid ionic compound. It is affected by several factors, including the charge and size of the ions. In general, as the charge on the ion increases, the lattice energy increases. Additionally, as the size of the ion decreases, the lattice energy increases.

Transition metals and their ions:

- Calcium (Ca) has a charge of +2 as an ion.
- Manganese (Mn) has a charge of +2 as an ion.
- Zinc (Zn) has a charge of +2 as an ion.
- Iron (Fe) has a charge of +3 as an ion.
- Gallium (Ga) has a charge of +3 as an ion.

Lattice energy curve:

The lattice energy curve shows the relationship between the charge on an ion and the corresponding lattice energy. In general, as the charge on the ion increases, the lattice energy also increases. However, there may be exceptions or deviations from this trend.

Number of transition metals ions on the straight line of lattice energy curve of their fluoride:

To determine the number of transition metal ions that lie on the straight line of the lattice energy curve of their fluoride, we need to compare the charges of the transition metal ions with their corresponding lattice energies.

- Calcium (Ca2+): The charge of +2 is relatively small, and its lattice energy may not lie on the straight line.
- Manganese (Mn2+): The charge of +2 is relatively small, and its lattice energy may not lie on the straight line.
- Zinc (Zn2+): The charge of +2 is relatively small, and its lattice energy may not lie on the straight line.
- Iron (Fe3+): The charge of +3 is larger than the previous ions, and its lattice energy may lie on the straight line.
- Gallium (Ga3+): The charge of +3 is larger than the previous ions, and its lattice energy may lie on the straight line.

Based on the analysis above, it can be concluded that 3 transition metal ions (Fe3+ and Ga3+) may lie on the straight line of the lattice energy curve of their fluoride. However, the lattice energies of calcium, manganese, and zinc ions may deviate from the trend.