Which of the following elements belongs to Group 2, Period 3?
A. Sr
B. Mg
C. Be
D. Ca
Answer: Option B
Solution (By JKSSB Mock Tests)
Magnesium (Z=12): configuration 2,8,2. Period = number of shells = 3; Group = 2 (2 valence electrons). Be is Group 2, Period 2; Ca is Group 2, Period 4; Sr Period 5.
Explanation:
This is a single displacement reaction. Iron (Fe) is more reactive than Copper (Cu), so it displaces copper from its aqueous sulfate solution. The blue color of CuSO₄ fades, and a brown deposit of Cu forms. Reactivity series dictates that a more reactive metal displaces a less reactive one.
Explanation:
Plaster of Paris (CaSO₄·½H₂O) reacts with water to form gypsum (CaSO₄·2H₂O) which sets into a hard solid mass with slight expansion. Reaction: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O. This property is used for casting and setting broken bones.
Explanation:
Ammonium ion (NH₄⁺) is formed when NH₃ donates its lone pair to H⁺, forming a coordinate (dative) bond. CH₄ and H₂O have ordinary covalent bonds; NaCl is ionic. In NH₄⁺, all four N–H bonds become equivalent.
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