Elements in the same group of the periodic table have the same:
A. Atomic mass
B. Number of valence electrons
C. Number of shells
D. Atomic radius
Answer: Option B
Solution (By JKSSB Mock Tests)
Elements in the same vertical column (group) have the same number of electrons in their outermost shell (valence electrons). This gives them similar chemical properties. The number of shells increases as we go down a group, leading to trends in atomic radius and ionization energy.
Explanation:
Evaporation of water is a physical change—liquid water changes to water vapor, but the chemical composition (H₂O) remains unchanged. Souring of milk and curd formation involve lactic acid bacteria converting lactose to lactic acid (chemical change). Fermentation of grapes involves yeast converting sugars to ethanol and CO₂. Chemical changes produce new substances. Physical changes only alter the state or form.
Explanation:
BF3 has a trigonal planar geometry with bond angles of 120 degrees. The three B-F bond dipoles are equal in magnitude and symmetrically arranged, so their vector sum cancels out completely, resulting in a net dipole moment of zero. H2S is bent, NF3 is pyramidal, and ClF3 is T-shaped.
Explanation:
Ethane: H₃C-CH₃. There is one C-C single bond and six C-H single bonds, total 7 covalent bonds. Each bond is a sigma bond. The structural formula shows 7 bonds. Methane has 4, propane 10. Counting bonds is simple: each line represents a covalent bond.
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