Could someone please tell me if I am correct on the following???:

Pick the larger species from each of the following pairs.

Sr or Sr^2+
*(I think it is Sr)

N or N^3-
*(I think it is N^3-)

Ni or Ni^2+
*(I think it is Ni)

S^2- or Ca^2+
*(I think it is S^2-)

You are correct for the first three. I THINK you are correct on the fourth but check some other sources.

the 4th one was correct as well. Thank you!

You are correct on all counts!

Sr is larger than Sr^2+.
N^3- is larger than N.
Ni is larger than Ni^2+.
S^2- is larger than Ca^2+.

To determine the larger species from each of the given pairs, we need to consider the electronic configuration and the number of electrons in each species.

1. Sr or Sr^2+:
- Sr (Strontium) is a neutral atom, so it has the electronic configuration 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2.
- Sr^2+ (Strontium ion) has lost two electrons, so it has the electronic configuration 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^6.

To determine the larger species, we need to compare the electron cloud size. Since Sr^2+ has lost two electrons, it has a smaller electron cloud than Sr. Therefore, you are incorrect in this case. The larger species is Sr (Strontium).

2. N or N^3-:
- N (Nitrogen) is a neutral atom, so it has the electronic configuration 1s^2 2s^2 2p^3.
- N^3- (Nitride ion) has gained three electrons, so it has the electronic configuration 1s^2 2s^2 2p^6.

To determine the larger species, again, we compare electron cloud size. Since N^3- has gained three electrons, it has a larger electron cloud than N. Therefore, you are incorrect in this case. The larger species is N^3- (Nitride ion).

3. Ni or Ni^2+:
- Ni (Nickel) is a neutral atom, so it has the electronic configuration 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8.
- Ni^2+ (Nickel ion) has lost two electrons, so it has the electronic configuration 1s^2 2s^2 2p^6 3s^2 3p^6 3d^8.

Ni^2+ has lost two electrons, so it has a smaller electron cloud than Ni. Therefore, you are correct in this case. The smaller species is Ni^2+ (Nickel ion).

4. S^2- or Ca^2+:
- S^2- (Sulfide ion) has gained two electrons, so it has the electronic configuration 1s^2 2s^2 2p^6 3s^2 3p^6.
- Ca^2+ (Calcium ion) has lost two electrons, so it has the electronic configuration 1s^2 2s^2 2p^6 3s^2.

To determine the larger species, we compare electron cloud size. Since S^2- has gained two electrons, it has a larger electron cloud than Ca^2+. Therefore, you are correct in this case. The larger species is S^2- (Sulfide ion).

Overall, you were incorrect for the first and second pairs but correct for the third and fourth pairs. Remember to consider the changes in electron configuration when determining the larger species.