In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Potassium ( K ) increment of 0 . 6 mEq / l or more was observed in 50 % of Group A , but in only 15 % of Group B patients ( p < 0 . 05 ) .
### Output Text:
<span class="chemical">Potassium</span> ( <span class="chemical">K</span> ) increment of 0 . 6 mEq / l or more was observed in 50 % of Group A , but in only 15 % of Group B patients ( p < 0 . 05 ) . 