In the modern periodic table, elements in the same group have the same:
A. Number of electron shells
B. Number of isotopes
C. Number of valence electrons
D. Atomic mass
Answer: Option C
Solution (By JKSSB Mock Tests)
Elements in the same group (vertical column) have the same number of valence electrons, resulting in similar chemical properties. For example, all Group 1 elements have 1 valence electron (ns¹). The number of shells increases down the group. Atomic mass varies. This similarity was the basis for Mendeleev's grouping. Modern table uses atomic number for ordering.
Explanation:
NH₄Cl is from HCl (strong) and NH₄OH (weak). Its aqueous solution is acidic due to hydrolysis of NH₄⁺. NaCl is neutral (strong-strong). CH₃COONa basic (weak-strong).
Explanation:
Graham's law: r₁/r₂ = √(M₂/M₁). Given rA/rB = 1/2, so √(MB/MA) = 1/2. Squaring: MB/MA = 1/4 => MB = MA/4 = 64/4 = 16 g/mol. B is lighter and diffuses faster. Logical check: rate inversely proportional to square root of molar mass; if rate is double, mass is quarter. Answer is 16.
Explanation:
Gypsum (CaSO₄·2H₂O) is added to clinker to control the rapid reaction of tricalcium aluminate with water, which would otherwise cause flash (quick) setting. Gypsum slows down the hydration of C₃A, thus increasing the setting time and allowing workability. Without gypsum, cement would set almost immediately upon mixing with water, making placement impossible.
No comments yet. Be the first to start the discussion!