Replace "CO2" by a "2" in subscript

[moussab33871616]

Hi everyone !
I have an InDesign document with more than 400 times "CO2". 
I absolutely need to replace all "CO2" by CO2 : the "2" has to be in subscript.
Is there a way to use the tool "Replace" with subscript ? 
Thanks

[Frans v.d. Geest · Accepted solution]

Use GREP!

Create a subscript character style, then create a Paragraph style that had that character style to be used with this GREP:

(?<=CO)2

Do you have NO2 and H2O as well? You can catch them all in one GREP:

([CN]O)\K2|(H)\K2(?=O)

[EDV5EB7]

How can this be solved so that the "2" is not shown as a subscript but as small capital?

[Rinwis4001]

When creating the character style, don't choose "position: subscript", but instead choose "Case: small caps". Both options can be found in the Character Styles Options menu, on the Basic Character Formats tab

[Rinwis4001]

I added ([cn]o)\K2|(h)\K2(?=o) to also apply this to all lowercase instances (co2, no2, h2o) too, but how do I capitalize the letters? Can I alter this GREP, do I make a new GREP?

[Rinwis4001]

In case anione else wonders, this is how I wound up doing it: I merged Frans' uppercase GREP and my lowercase GREP together into:

((?i)[CN](?i)O)\K2|((?i)H)\K2(?=(?i)O)

and I added a new GREP to capitalize all lowercase instances:

(?i)[cn]o(?=2)|(?i)h(?=2)|(?<=2)o

There might be a more effcient GREP string, but this seems to be working