Correct Answer - Option 4 : 2.0 × 10

^{-17} J

**Concept:**

**Photon**

- A photon is a
**packet of energy that forms light. **
- Each photon has energy E = h ν where ν is the frequency of the wave, h is Planck's constant.
- The energy can also be represented as

\(E = h\frac{c}{λ }\)

where λ is the wavelength, c is the speed of light,

c = 3 × 10 ^{8} m /s

**Calculation:**

Given,

Wavelength λ = 100 Å

1 Å = 10^{ -10} m

So, wavelength in meter

λ = 100 Å = 10 ^{2} × 10 -10 = 10 ^{-8} m

The energy can also be represented as

\(E = h\frac{c}{λ }\)

\(\implies E = (6.626 × 10 ^{-34})\frac{3 × 10^8}{10^{-8} } J\)

⇒ E = 19.878 × 10^{ (-34 + 8 + 8 )} J = 19.878 × 10 ^{- 18} Joule

⇒ E ≈ 2.0 × 10-17 Joule

**So, the correct option is 2.0 × 10-17 J**