What element is in period 4 and has 4 number shells and 3 valence electrons?

The valency and valency shell of an element can be determined by its electronic configuration. It refers to the distribution of electrons revolving around the nucleus of an element in its shells. These energy levels are represented by an integer known as the principle quantum number represented by the symbol n. 

In the given question it is given that the element has 4 shells and  3 electrons in its outermost or valency shell meaning that the first 3 shells are completely filled. 

By this we can calculate total number of electrons which are K = 2, L = 8, M = 18 so, 2+8+18+3(valence electrons) = 31. 

We know that the atomic number of an element can be determined if we know the number of protons or electrons preset in that element as it is equal to its number of protons/electrons which is calculated as 31. 

So, the atomic number of this element is 31. The atomic number of Gallium is 31 also it belongs to 4th period which verifies that the given element is Gallium represented by Ga.

Hence, option D is correct.