Correct Answer:
(D)
Melting of ice
. Melting ice is a physical change, where the state of matter changes from solid to liquid, but the chemical composition of the water remains the same.
Ques:
52
A mixture of sand and naphthalene can be separated by :
Correct Answer:
(A)
Sublimation
Naphthalene displays the phenomenon of sublimation, which is the transition of a substance directly from the solid to gas phase upon heating. Hence, a mixture of sand and naphthalene can be separated by sublimation.
Ques:
53
Match List-I (oxidation number) with List-II (the element) and select the correct answer using the codes given below the lists :
List-I (Oxidation Number) List-II ( The Element)
A. 2 1. Oxidation number of Mn in MnO2
B. 3 2. Oxidation number of S in H2SO4
C. 4 3. Oxidation number of Ca in CaO
D. 6 4. Oxidation number of Al in NaAlH4
Code :
A B C D
Correct Answer:
(A)
3 4 1 2
In the given solution, A-3 correctly pairs the oxidation number 2 with calcium in CaO₂, which is accurate since calcium commonly exhibits a +2 oxidation state. B-4 links oxidation number 3 with aluminum in NaAlH₄, and this is also correct as aluminum has a +3 oxidation state in this compound. C-1 matches oxidation number 4 with manganese in MnO₂, which is valid because manganese has a +4 oxidation state here. Finally, D-2 pairs oxidation number 6 with sulfur in H₂S₂O₇, where sulfur indeed shows a +6 oxidation state.
Thus, the correct matching is A-3 (calcium, +2), B-4 (aluminum, +3), C-1 (manganese, +4), and D-2 (sulfur, +6), making option 1 the right answer.
Ques:
54
Example of corrosion is –
Correct Answer:
(D)
Above three
Gradual decay of metals by air or chemical substances is called corrosion. Rusting on iron i.e. brown coating on iron, green coating on copper and black coating on silver, all these are examples of corrosion.