The atomic number of an element is 19. based on its electron arrangement, which of the following explains its correct position in the periodic table? group 1, because it has a single electron in the 4s orbital. group 4, because it has a single electron in the 4s orbital. group 1, because its last electron is in the 3s orbital. group 4, because its last electron is in the 4s orbital.

The first answer in my opinion correct me if im wrong..

 Group 1, because it has a single electron in the 4s orbital

Explanation:  Atomic number and electronic configuration of an element is the characteristic property of that element.

Electronic configuration also helps us to know the group to which the element belongs.

Here the atomic number given is 19. And as we know noble gas element Argon has the atomic number 18 which has complete electronic valence shell with configuration 1s2 2s2 2p6 3s2 3p6.

Thus the next electron will enter the 4s subshell and will contain 1 electron for atomic number 19 with electronic configuration 1s2 2s2 2p6 3s2 3p6 4s1 .

Thus element with atomic number 19 will belong to the Group 1 because it has single electron in the 4s orbital.