Consider the following statements about the modern periodic table: 1. Elements are arranged by atomic mass. 2. It has 18 groups and 7 periods. 3. The f-block elements are called inner transition metals. Which are correct? MCQ with Answer and Explanation
Consider the following statements about the modern periodic table: 1. Elements are arranged by atomic mass. 2. It has 18 groups and 7 periods. 3. The f-block elements are called inner transition metals. Which are correct?
A. 1 and 3 only
B. 1 and 2 only
C. 1, 2 and 3
D. 2 and 3 only
Answer: Option D
Solution (By JKSSB Mock Tests)
The modern periodic table is based on atomic number, not atomic mass (Mendeleev's table was based on mass). It consists of 18 vertical groups and 7 horizontal periods. The f-block elements, placed at the bottom, are indeed called inner transition metals (lanthanides and actinides). Thus, statements 2 and 3 are correct.
Explanation:
The ozone layer is located in the lower stratosphere (~15-35 km altitude), where ozone concentration is highest. It absorbs harmful ultraviolet radiation (UV-B and UV-C) from the sun. Ground-level ozone (troposphere) is a pollutant and component of smog, harmful to health. Ozone depletion is caused by chlorofluorocarbons (CFCs) which release chlorine atoms that catalytically destroy O₃.
Explanation:
Inhibitors (negative catalysts) decrease reaction rate. Promoters enhance activity of a catalyst; activators increase effectiveness; autocatalysts are reaction products that catalyze the reaction.
Explanation:
Portland cement primarily consists of calcium silicates (C₃S and C₂S) along with aluminates. These are formed by heating limestone and clay.
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