Which metal is used in the thermal process for welding railway tracks? MCQ with Answer and Explanation

Explanation:
Ionic character increases with the difference in electronegativity between bonding atoms. In hydrogen halides, electronegativity decreases from F to I (F: 4.0, Cl: 3.0, Br: 2.8, I: 2.5). Thus HF has the largest electronegativity difference (1.9) and highest ionic character. The trend: HF > HCl > HBr > HI. However, HF is still a covalent polar molecule. Exam tip: Electronegativity difference > 1.7 usually indicates ionic bond.

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.

Explanation:
J.J. Thomson discovered the electron through cathode ray tube experiments in 1897 and measured the e/m ratio by applying electric and magnetic fields. Rutherford discovered the nucleus via the gold foil experiment. Chadwick discovered the neutron (1932). Bohr proposed the planetary model of the atom with quantized orbits. Thomson's model (plum pudding) was later superseded. Exam memory: Thomson = electron (e/m); Rutherford = nucleus; Chadwick = neutron; Bohr = energy levels.