0.Assertion: Nickel is a transition element which belongs to group 10 and period 4 of modern periodic table                                                                              Reason: Electronic configuration of Ni is [Ar]3d8

The assertion and the reason are both correct. Nickel is indeed a transition element that belongs to group 10 and period 4 of the modern periodic table. This is due to its electronic configuration, which is [Ar]3d8.

Here's a step-by-step explanation:

1. The modern periodic table is organized in such a way that elements with similar properties are grouped together. Transition elements are found in groups 3-12.

2. Nickel, with the atomic number 28, is located in group 10 and period 4 of the periodic table.

3. The electronic configuration of an element explains its position in the periodic table. The electronic configuration of Nickel is [Ar]3d8.

4. The [Ar] represents the electron configuration of the noble gas Argon, which precedes Nickel in the periodic table. The 3d8 means there are 8 electrons in the 3d orbital.

5. The electron configuration confirms Nickel's position in the periodic table. The 3d8 configuration means it is in the d-block, which is where the transition metals are located. The fact that it has 8 electrons in the 3d orbital places it in group 10.

6. Therefore, the assertion that Nickel is a transition element in group 10 and period 4 of the periodic table is correct, and the reason given (its electronic configuration) is accurate.