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: Ifosfamide ( IFO ) is an alkylating nitrogen mustard , administrated as an antineoplasmic agent .
### Output Text:
<span class="chemical">Ifosfamide</span> ( <span class="chemical">IFO</span> ) is an alkylating <span class="chemical">nitrogen</span> mustard , administrated as an antineoplasmic agent . 