In which group of the periodic table is Ni placed?

Think it through first, then pick an option.

Answer and explanation

Correct answer: c 10

Ni (28) is 3d⁸4s²; by rule 3 the group = d electrons + s electrons = 8 + 2 = 10.

Why the other options are wrong

a 2: Group 2 holds elements like Mg and Ca, which have no d electrons; Ni is 3d⁸4s², so it is not in group 2.
b 4: Group 4 is Ti (3d²4s²), with 2 electrons in d; Ni has 8 in d, so 8 + 2 = 10.
d 12: Group 12 is Zn (3d¹⁰4s²), with a full d; Ni has 8 electrons in d, not 10.