Correct Option
The correct option is Silver chloride and silver bromide.
Explanation
Black and white photography relies on the photosensitive nature of specific chemical compounds known as silver halides. These compounds undergo a chemical change known as photolytic decomposition when exposed to light.
Detailed Analysis
- Silver Chloride (AgCl) and Silver Bromide (AgBr): These compounds are highly sensitive to light. When light falls on photographic film or paper coated with these salts, they decompose into silver metal and halogen gas (chlorine or bromine).
- The Chemical Reaction: The reaction is an example of a decomposition reaction driven by light energy.
2AgCl(s) $\xrightarrow{\text{Sunlight}}$ 2Ag(s) + Cl$_2$(g)
2AgBr(s) $\xrightarrow{\text{Sunlight}}$ 2Ag(s) + Br$_2$(g) - Result: The metallic silver (Ag) produced in this reaction turns grey or black, creating the dark parts of a photographic image corresponding to the intensity of light exposure.
- Incorrect Options: Sodium chloride, potassium bromide, and lead chloride do not exhibit the specific light-sensitive decomposition required for photographic emulsions.
Key Takeaway: Silver chloride and silver bromide are used in black and white photography due to their ability to undergo photolytic decomposition, turning into metallic silver upon exposure to light.