The half-life of a radioactive isotope is 10 years. What fraction of the original sample will remain after 30 years?
A. 1/8
B. 1/4
C. 1/16
D. 1/2
Answer: Option A
Solution (By JKExamLibrary)
The half-life is the time required for half of the radioactive atoms to decay. After 10 years (1 half-life), 1/2 remains. After 20 years (2 half-lives), 1/4 remains. After 30 years (3 half-lives), the fraction remaining is (1/2)^3 = 1/8. Thus, one-eighth of the original sample will remain.
Explanation:
In NO₂, each oxygen has valency 2; with two oxygens, total combining capacity = 4. Thus nitrogen's covalency is 4. The structure involves a coordinate bond. Oxidation state of N is +4. Valency is number of bonds formed: N forms two single bonds and one coordinate bond with O, total 4 bonds. In NO, valency is 2.
Explanation:
Naphthalene sublimes on heating, directly changing to vapor, while sand remains. The naphthalene vapor can be condensed on a cold surface. This technique works for any mixture where one component sublimes (naphthalene, camphor, NH₄Cl). Filtration works for insoluble solids in liquids. Magnetic separation for magnetic ores. Distillation for liquid mixtures.
Explanation:
Graphite, an allotrope of carbon, is a good conductor of electricity. This is because each carbon atom is bonded to three others, leaving one free valence electron per atom that is delocalized and can move freely between the layers to conduct electricity, unlike diamond which is an insulator.
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