1995 General Studies, all questions
UPSC Prelims 1995 · General Studies
Question 103: Science and Technology
The chemical used as a ‘fixer’ in photography is
asodium sulphate
bsodium thiosulphate
cammonium persulphate
dborax
AnswerThe answer is (b).
In photography, the developer turns the exposed silver halide into black silver. The fixer then dissolves the unexposed silver halide so that the image does not darken further in light. Sodium thiosulphate, called hypo, does this by forming a soluble complex with silver salts. Remember: hypo is the fixer.
Why each option is right or wrong
- (a) Sodium sulphate is not a fixer.
- (b) Right: sodium thiosulphate, or hypo.
- (c) Ammonium persulphate is an oxidising agent used in other roles, not a fixer.
- (d) Borax is sometimes used in developers as an alkali, not as a fixer.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1995, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.