Question

Silver halides are used in photography because they are:
A.Photosensitive
B.Soluble in hypo solution
C.Soluble in $N{H_4}OH$
D.Insoluble in acids\[\]

Answer 1

Hint: Silver halides ($AgX$ ) are ionic crystals consisting of a regular cubic lattice of $Ag$ and halide ions together with a small proportion of defects, such as $Ag$ ions that have been displaced from their regular lattice position to another “interstitial” position (the Ag ions are much smaller than the halide ions), and the corresponding vacancy in the lattice.

Complete step by step answer:
Silver halides are used in photography because they are photosensitive as they react with light to form the image, silver halides being reduced to silver.

Hence the correct option is (A).
In $AgX$, all the energy levels of the highest occupied energy band (the valence band, VB) are filled with electrons. Although the electrons are delocalized, any increase of one electron's momentum under the action of an electric field must be balanced by a reduction of momentum of another one, because spare energy states are available. Thus, in a perfect crystal, essentially no electronic conduction occurs. The next higher energy band (the conduction band, CB) is essentially empty in a perfect $AgX$ crystal, being too far (2.5 eV or so) above the VB for significant thermally excited transitions to take place from the VB. In a perfect crystal, there are no energy levels in the gap between the VB and CB, but in real microcrystals there are a few such levels associated with crystal defects. These defect states are critical to photosensitivity. It has been shown experimentally that the purest, most perfect crystals of $AgX$ are virtually insensitive to light.

Note:
Silver halides, except for silver fluoride, are very insoluble in water. Silver nitrate can be used to precipitate halides; this application is useful in quantitative analysis of halides. The three main silver halide compounds have distinctive colors that can be used to quickly identify halide ions in a solution. The silver chloride compound forms a white precipitate, silver bromide a creamy colored precipitate and silver iodide a yellow colored precipitate. They are also soluble in hypo solution.