Question

part b true - false
classify each of these statements as always true, at; sometimes true, st; or never true, nt.
____ 13. in his periodic table, mendeleev arranged the elements in ascending order of atomic number.
____ 14. the representative elements are the group a elements.
____ 15. the transition metals and inner transition metals are the group b elements.
____ 16. the element in group 4a, period 3, is gallium.

Explanation:

Step1: Mendeleev's periodic table

Mendeleev arranged elements in ascending order of atomic mass. Atomic number concept came later. So statement 13 is never true.

Step2: Representative elements

Representative elements are Group A elements. This is a standard definition. So statement 14 is always true.

Step3: Transition and inner - transition metals

Transition metals (d - block) and inner - transition metals (f - block) are not Group B elements. Group B is a misnomer in modern terms. So statement 15 is never true.

Step4: Element in Group 4A, period 3

In Group 4A (14th group) and period 3, the element is silicon (\(Si\)), not gallium (\(Ga\)). Gallium is in Group 3A (13th group), period 4. So statement 16 is never true.

Answer:

1. NT
2. AT
3. NT
4. NT