Question

According to Mendeleev’s periodic table, one element whose atomic mass is greater than that of nickel is placed before Nickel. Name the element:
A. Copper
B. Iron
C. Zinc
D. Cobalt

Answer 1

We know that there were many attempts in the 17th century to classify elements, such as Dobereiner’s triads, Newlands law of octaves etc. But Dmitri Mendeleev was the first to make a very significant contribution in classification of elements.

Complete step by step answer:
Mendeleev studied the chemical properties of a large number of elements and in 1869 came out with a statement that properties (physical or chemical) of elements are periodic functions of atomic masses of them. This is called Mendeleev's periodic law.
So, from Mendeleev’s law, both physical and chemical properties of elements get repeated after certain definite intervals. He arranged all the elements known at that time in order of increasing atomic mass and this arrangement is known as periodic table. The vertical rows are called as groups and horizontal columns are called as periods.
But there are many defects in the Mendeleev’s periodic table, such as anomalous positions of some elements. In some cases, an element possessing higher atomic mass precedes the element possessing lower atomic mass. For example, Argon (Ar) of atomic mass 39.9 precedes potassium (K) of atomic mass 39.1. Similarly, Cobalt (Co) of atomic mass 58.9 is placed before Nickel (Ni) of atomic mass 58.7.

So, the correct answer is Option D.

Note:
Mendeleev’s periodic table helps to systematically study elements. While framing the periodic table, he laid more stress on similarity of properties rather than increasing atomic mass of elements, so he left a gap whenever a particular element did not fit the arrangements. So, prediction of new elements and properties is easier.