Arrange the members of the following set of cations in order of increasing ionic radii:

Sr2+
Ba2+
Rb+
K+
I understand that Sr2+ = 132 pm
Ba2+ = 149 pm
Rb+ = 166 pm
K+ = 152 pm

increasing ionic radii ....Sr2+ , Ba2+ , K+, Rb+
But the its not going in online as correct

Well, it looks like those cations are just not taking the hint to arrange themselves in increasing order of ionic radii. Perhaps they're feeling a bit rebellious today. But fear not, for Clown Bot is here to sort things out!

Let's put on our clown spectacles and analyze this with a comedic twist.

First up, we have Mr. Sr2+, who strolls onto the stage with a diameter of 132 pm. He is a smaller cation, always aiming to make a grand, refined entrance.

Next in line is Mr. Ba2+. With a slightly bigger diameter of 149 pm, he's like Sr2+'s younger brother who's trying to outshine his sibling by being a tad larger.

Now, let's welcome our energetic duo: Mr. K+ and Mr. Rb+. These two jokers have similar diameters, with K+ measuring in at 152 pm and Rb+ being a touch larger at 166 pm. They're like a comedy duo, constantly trying to one-up each other in size and outrageous antics.

So, the correct order of increasing ionic radii is:
Sr2+ < Ba2+ < K+ < Rb+

And there you have it! Clown Bot has saved the day once again, bringing a bit of laughter to the world of chemistry.

The correct order of increasing ionic radii for the given cations is:

Rb+ > K+ > Sr2+ > Ba2+

This is because as you move across a period in the periodic table (from left to right), the atomic radius decreases due to increased nuclear charge. On the other hand, as you move down a group (from top to bottom), the atomic radius increases due to the addition of new electron shells.

To arrange the cations in order of increasing ionic radii, you need to consider the trends in the periodic table. The ionic radii generally increase as you go down the periodic table within a group and decrease as you go from left to right across a period.

In this case, we have Sr2+, Ba2+, Rb+, and K+. We can see that Sr2+ and Ba2+ are in the same group (Group 2) and that Rb+ and K+ are in the same group (Group 1) as well.

In Group 2, as you move down the periodic table, the ionic radii increase due to the addition of more electron shells. Thus, Sr2+ (132 pm) has a smaller ionic radius compared to Ba2+ (149 pm). Therefore, we can determine that Ba2+ has a larger ionic radius than Sr2+.

Similarly, in Group 1, as you move down the periodic table, the ionic radii also increase. Therefore, K+ (152 pm) has a smaller ionic radius than Rb+ (166 pm). This means that Rb+ has a larger ionic radius than K+.

Putting it all together, the correct order of the cations in terms of increasing ionic radii is:

Sr2+ < Ba2+ < K+ < Rb+.

It's possible that the online platform or system you used might have a different expected answer format, so double-check the instructions provided and make sure you are entering the answer correctly.

Where did your numbers for radius come from? They must not agree with the data base? So where do the numbers the data base is using come from?

My inclination, which doesn't agree with your numbers,
K+ is the smallest. You know Rb+ must be larger. You know Sr must be smaller than Rb so we have K^+ to Sr^2+ to Rb^+. That leaves Ba^2+ to be placed. Since that is another complete shell larger I think that must go above Rb. I would place these as
K, Sr, Rb, Ba from lowest to highest I think the ONLY way to do this, considering that ionic ion measurements are so uncertain, is to use the same system the database is using.