The disinfection method that leaves no residual effect in water is: MCQ with Answer and Explanation

Explanation:
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:
Ernest Rutherford, through the gold foil experiment in 1911, discovered the dense, positively charged nucleus. Thomson discovered the electron, Bohr proposed quantized orbits, Chadwick discovered the neutron. Rutherford also discovered the proton.

Explanation:
Oxidation of ethanol with acidified K₂Cr₂O₇ or KMnO₄ produces ethanoic acid (CH₃COOH). Dehydration gives ethene; hydrogenation adds H₂; fermentation produces ethanol from sugars.