Question

Which of the following is NOT a reason why Cobalt and Nickel in the fourth period violate the original periodic law as stated by Mendeleev?

(a) Their atomic masses are in the wrong order.
(b) Their chemical properties are more similar to each other than to the other elements in their respective groups.
(c) Their atomic radii are too similar to each other.
(d) They both have 18 electrons in their outermost shell.

Answer 1

The element that does not violate the original periodic law for Cobalt and Nickel is that they both have 18 electrons in their outermost shell.

Step-by-step explanation:

The correct answer is (d) They both have 18 electrons in their outermost shell.

According to the original periodic law stated by Mendeleev, elements were arranged in order of increasing atomic mass. However, Cobalt (atomic number 27) and Nickel (atomic number 28) violate this rule because their atomic masses are not in the correct order. Cobalt has a slightly higher atomic mass than Nickel, but it is placed before Nickel in the periodic table due to their similar chemical properties.

Therefore, option (d) is the correct answer as it does not violate the original periodic law.