Question

Part A

What observations led to the periodic law?

A.) observation that the properties of elements recure and certain elements have similar properties

B.) observation that the all halogen elements have similar properties

C.) observation that certain elements possess such property as radioactivity

D.) observation that the all metals have similar properties

Part B

What theory explains the underlying reasons for the periodic law?

A.) Lewis theory

B.) quantum-mechanical theory

C.) atomic theory

D.) Brønsted–Lowry theory

Answer 1

1)Periodic table was first framed by mendeleev, by the principle followed by Doberiner and newland.

Periodic table was 1st framed because it was difficult to remember all 118 element in series.

Scientists found that certain element possess similar properties.

Thus answer is A where it was observed that properties of element recure and certain element have similar properties.

2)The theory that explains the underlying reason feature of periodic law is quantum mechanical theory.