**Bond Dissociation Energy**

The bond dissociation energy (BDE) is the amount of energy required to break a chemical bond. It represents the strength of the bond and is usually measured in units of kilojoules per mole (kJ/mol).

In the given problem, the bond dissociation energy of AB molecules is stated to be 300 kJ/mol. This means that 300 kJ of energy is required to break one mole of AB molecules into their constituent atoms.

**Calculating Energy per Molecule**

To calculate the energy required to dissociate 3 moles of AB molecules, we need to determine the total energy required.

1 mole of AB molecules requires 300 kJ of energy to dissociate.

Therefore, 3 moles of AB molecules will require:

3 moles x 300 kJ/mole = 900 kJ

So, 900 kJ of energy is required to dissociate 3 moles of AB molecules.

**Calculating Energy per Photon**

To calculate the number of photons required, we need to relate the energy of a single photon to the total energy required.

The energy of a photon can be calculated using the equation:

E = hc/λ

Where:
E = energy of photon (in joules)
h = Planck's constant (6.626 x 10^-34 J.s)
c = speed of light (3.00 x 10^8 m/s)
λ = wavelength of the photon (6625 Å)

Converting the wavelength to meters:

λ = 6625 Å x (1 m/10^10 Å) = 6.625 x 10^-7 m

Substituting the values into the equation:

E = (6.626 x 10^-34 J.s) x (3.00 x 10^8 m/s) / (6.625 x 10^-7 m)

E ≈ 2.998 x 10^-19 J

Converting the energy to kilojoules:

E = 2.998 x 10^-19 J x (1 kJ/1000 J) = 2.998 x 10^-22 kJ

**Calculating the Number of Photons**

To calculate the number of photons required, we divide the total energy required (900 kJ) by the energy per photon (2.998 x 10^-22 kJ):

Number of photons = 900 kJ / (2.998 x 10^-22 kJ)

Number of photons ≈ 3.003 x 10^25 photons

Therefore, approximately 3.003 x 10^25 photons of wavelength 6625 Å are required to dissociate 3 moles of AB molecules.