In this task, you are given a context, a subject, a relation, and many options. Based on the context, from the options select the object entity that has the given relation with the subject. Answer with text (not indexes).
Q: Context: A phosphite in inorganic chemistry is a salt of phosphorous acid, HPO and following the IUPAC naming recommendations the phosphite ion would be , a salt of P(OH)., Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but only the gray form is important to industry., In chemistry, an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble As anions. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-arsenatite is called trioxidoarsenate(III).
Ortho-arsenite contrasts to the corresponding anions of the lighter members of group 15, phosphite which has the structure and nitrite, which is bent., The arsenate ion is .
An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid.
The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V).
Arsenate resembles phosphate in many respects, since arsenic and phosphorus occur in the same group (column) of the periodic table. 
Arsenates are moderate oxidizers, with an electrode potential of +0.56 V for reduction to arsenites., Potassium arsenite ( KAsO2 ) is an inorganic compound that exists in two forms , potassium meta - arsenite ( KAsO2 ) and potassium ortho - arsenite ( K3AsO3 ) . It is composed of arsenite ions ( AsO33  or AsO2  ) with arsenic always existing in the +3 oxidation state , and potassium existing in the +1 oxidation state . Like many other arsenic containing compounds , potassium arsenite is highly toxic and carcinogenic to humans . Potassium arsenite forms the basis of Fowler 's solution , which was historically used as a medicinal tonic , but due to its toxic nature its use was discontinued . Potassium arsenite is still , however , used as a rodenticide ., The nitrite ion, which has the chemical formula , is a symmetric anion with equal NO bond lengths. Upon protonation, the unstable weak acid nitrous acid is produced. Nitrite can be oxidized or reduced, with the product somewhat dependent on the oxidizing/reducing agent and its strength. The nitrite ion is an ambidentate ligand, and is known to bond to metal centers in at least five different ways. Nitrite is also important in biochemistry as a source of the potent vasodilator nitric oxide. In organic chemistry the NO group is present in nitrous acid esters and nitro compounds. Nitrites are also used in the food production industry for curing meat., Subject: potassium arsenite, Relation: instance_of, Options: (A) acid (B) anion (C) chemical compound (D) chemical element (E) column (F) combination (G) crystal (H) electrode (I) formula (J) industry (K) ion (L) meat (M) note (N) number (O) oxide (P) phosphate (Q) product (R) salt (S) state
A:
chemical compound