As the first five elements in group 15 are considered in order of increasing atomic number, first ionization energy increases, then decreases decreases, then increases decreases increases

the first ionization energy decreases.

Justification:

1) The group 15 is formed by N, P, As, Sb, Bi, and Mc.

2) The first ionization energy is defined as the energy needed to remove an electron from the neutral atom in the gas state.

3) The elements of the group 15 have the following general electron configuration for the valence shell: ns² np³. Where n is the principal quantum number (the same number of the row in which the element is).

4) As you go down in the group, n increases, and the valence electrons are further away of the nucleous, meaning that those electrons are lessen attracted to the nucleous.

Consequently, as you go down in the group, the electrons will be removed more easily, i.e less energy will be required to get them removed.

5) That permits you to predict this order in the first ionization energies: N > P > As > Sb > Bi > Mc.

And that agrees with the data that you can find in a table of first ionization energies.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.