Arrange the following compounds of Arsenic in increasing order of their LD50 (mg/kg):

A. Arsenous Acid H₃AsO₃

B. Arsenic Acid H₃AsO4

C. Arsenocholine (CH3)3As+CH2CH2OH

D. Dimethylarsinic Acid (CH3)2AsO(OH)

E. Arsenobetaine (CH3)3As+CH2COO

Choose the correct answer:

Correct option is D

Introduction:

• Arsenic compounds can be broadly categorized as inorganic and organic. Inorganic arsenic compounds are generally more toxic than organic arsenic compounds.
• Within inorganic arsenic, the trivalent form (like in arsenous acid) is typically considered more toxic than the pentavalent form (like in arsenic acid).
• Organic arsenic compounds, such as arsenocholine and arsenobetaine, are generally considered to be of much lower toxicity and are often readily excreted by the body.

• The order of increasing LD50 (from most toxic to least toxic) for the given compounds is:
• A. Arsenous Acid (H₃AsO₃) - Trivalent inorganic arsenic, generally most toxic.
• B. Arsenic Acid (H₃AsO₄) - Pentavalent inorganic arsenic, less toxic than the trivalent form.
• D. Dimethylarsinic Acid ((CH₃)₂AsO(OH)) - An organic arsenic compound, significantly less toxic than inorganic forms.
• C. Arsenocholine ((CH₃)₃As⁺CH₂CH₂OH) - An organic arsenic compound, with low toxicity.
• E. Arsenobetaine ((CH₃)₃As⁺CH₂COO) - A very low toxicity organic arsenic compound.
• Thus, the correct arrangement in increasing order of LD50 is:
• Arsenous Acid < Arsenic Acid < Dimethylarsinic Acid < Arsenocholine < Arsenobetaine 
• A. Arsenous Acid (H₃AsO₃) < B. Arsenic Acid (H₃AsO₄) < D. Dimethylarsinic Acid ((CH₃)₂AsO(OH)) < C. Arsenocholine ((CH₃)₃As⁺CH₂CH₂OH) < E. Arsenobetaine ((CH₃)₃As⁺CH₂COO).
• The toxicity of arsenic compounds is influenced by their chemical form. Inorganic arsenic is more toxic than organic arsenic.
• Trivalent inorganic arsenic is generally more toxic than pentavalent inorganic arsenic.
• Organic arsenic compounds like arsenocholine and arsenobetaine are typically well-tolerated and rapidly excreted, resulting in much higher LD50 values (lower toxicity) compared to inorganic forms.