A green leaf has a surface area of 2.40 cm^2.

To determine the number of photons that strike the leaf every second, we need to use the formula:

Number of photons = (Power / Energy per photon) x Leaf area,

where:
- Power is the solar radiation (1120 W/m^2),
- Energy per photon is the energy associated with each photon,
- Leaf area is the surface area of the green leaf (2.40 cm^2).

To find the energy per photon, we can use Planck's equation:

Energy per photon = Planck's constant × speed of light / wavelength,

where:
- Planck's constant (h) is approximately 6.63 × 10^-34 J·s,
- Speed of light (c) is approximately 3 × 10^8 m/s,
- Wavelength is the average wavelength of solar radiation (504 nm = 504 × 10^-9 m).

Let's plug in the values and calculate:

Energy per photon = (6.63 × 10^-34 J·s) × (3 × 10^8 m/s) / (504 × 10^-9 m)
≈ 3.94 × 10^-19 J.

Converting the leaf area from cm^2 to m^2:

Leaf area = 2.40 cm^2 ≈ 2.40 × 10^-4 m^2.

Now we can substitute all the values into the initial formula:

Number of photons = (1120 W/m^2 / 3.94 × 10^-19 J) × (2.40 × 10^-4 m^2)
≈ 6.79 × 10^17 photons.

Therefore, approximately 6.79 × 10^17 photons strike the green leaf every second under the given conditions.