The atomic radius of elements decreases across a period because:
A. Atomic mass decreases
B. Number of shells increases
C. Electron-electron repulsion decreases
D. Nuclear charge increases and electrons are added to the same shell
Answer: Option D
Solution (By JKSSB Mock Tests)
Across a period, the number of electron shells remains the same, but the nuclear charge (protons) increases. The added electrons enter the same valence shell, so the effective nuclear attraction on the electrons increases, pulling them closer and shrinking the atomic radius. Down a group, radius increases due to addition of shells. Electron-electron repulsion alone does not account for the trend. Atomic mass generally increases across a period.
Explanation:
Zn + 2HCl → ZnCl₂ + H₂↑. Zinc displaces hydrogen from acid because it is more reactive than hydrogen in the reactivity series. Hydrogen gas burns with a pop sound when a burning splint is brought near the mouth of the test tube. Metals above hydrogen in the series react with acids to evolve H₂; metals below (Cu, Ag) do not. Nitric acid is an oxidizer, so may not yield H₂.
Explanation:
Electrolysis uses an external electric current to drive a chemical reaction that would not occur spontaneously. Example: 2NaCl (molten) → 2Na + Cl₂. Option A describes a galvanic cell. Electrolytic cells require energy input. Electroplating, extraction of reactive metals (Al, Na), and production of chemicals (NaOH, Cl₂) rely on electrolysis.
Explanation:
Luster is a characteristic physical property of metals, but some non-metals also exhibit a shiny appearance. Iodine is a non-metal that forms dark purple, lustrous crystalline solids. Sulphur is dull yellow, phosphorus is white/red and waxy, and carbon (as graphite/coal) is generally dull.
No comments yet. Be the first to start the discussion!