Q.Explain, with two historical examples, how Moseley's law resolved anomalies in the periodic table that had arisen from ordering elements strictly by atomic mass.

Before Moseley's measurements, elements were ordered in the periodic table by increasing ATOMIC MASS, since atomic number had no direct experimental measurement of its own. This produced a few stubborn anomalies where the chemically correct order (matching each element's family/valence behaviour) did not match strict mass order: cobalt (mass $58.93$) must chemically come BEFORE nickel (mass $58.69$), even though cobalt's mass is slightly larger; argon (mass $39.95$) must come before potassium (mass $39.10$); tellurium (mass $127.60$) must come before iodine (mass $126.90$) -- in each pair, strict mass ordering would put them the wrong way round. …

State the mass-based rule that was used before Moseley, give the specific pairs where it fail …

• Giving only one example instead of the (syllabus-expected) two, or giving vague examples without the actual mass/Z values. …