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Oxidation number determination including fractional and unusual cases

58 questions on Oxidation number determination including fractional and unusual cases from the Basic Inorganic Nomenclature and Oxidation Number chapter: 11 NEET level, 23 JEE Main, 24 JEE Advanced. Each one opens with its answer and solution.

Practice this topic All Basic Inorganic Nomenclature and Oxidation Number topics

What is the oxidation number of manganese in KMnO4? NEET level
What is the oxidation number of hydrogen in lithium hydride, LiH, a saline (metal) hydride? NEET level
What is the oxidation number of nitrogen in the ammonium ion, NH4+? NEET level
What is the oxidation number of phosphorus in phosphoric acid, H3PO4 (H is +1, O is -2)? NEET level
What is the oxidation number of sulfur in the sulfite ion, SO3^2- (O is -2)? NEET level
Find the AVERAGE oxidation number of sulfur in the tetrathionate ion S4O6^2- (O is -2). JEE Main level
Bleaching powder, CaOCl2, is treated as the mixed salt Ca(OCl)Cl, containing Ca^2+, OCl- and Cl- ions. What are the oxidation numbers of the two chlorine atoms ... JEE Main level
Carbon suboxide has the formula C3O2 (O is -2). What is the AVERAGE oxidation number of carbon? JEE Main level
Chromium pentoxide, CrO5, has two peroxo (O-O) groups and one oxo O atom (peroxo O is -1, oxo O is -2). What is the oxidation number of chromium? JEE Main level
Sodium nitroprusside is Na2[Fe(CN)5(NO)]. Treat each cyanide as CN- and the nitrosyl ligand as the nitrosonium cation NO+. What is the oxidation number of iron? JEE Main level
What is the oxidation number of carbon in dichloromethane, CH2Cl2 (H is +1, Cl is -1)? JEE Main level
Assertion (A): The average oxidation number of sulfur in S4O6^2- is +2.5, a fraction, although no individual sulfur atom can have a fractional oxidation number.... JEE Main level
Match the species in Column I with the oxidation number of the named metal in Column II (CN is CN-, CO is a neutral ligand). Column I: (P) Fe in K4[Fe(CN)6]; (Q... JEE Main level
In which of the following does nitrogen have the oxidation number -2 (H is +1, O is -2, Na is +1)? JEE Main level
Select the species in which the named element has a NON-INTEGER (fractional) average oxidation number (H is +1, O is -2). JEE Main level
Select the species in which the AVERAGE oxidation number of carbon is zero (H is +1, O is -2, Cl is -1; in CaC2, Ca is +2). JEE Main level
An oxide of iron contains 72.4% Fe by mass (Fe =56, O =16). Find its simplest formula and then the AVERAGE oxidation number of iron in it (O is -2 and there is ... JEE Advanced level
Arrange the oxidation numbers of nitrogen in the following compounds in increasing order (H is +1, O is -2; use the average value for HN3). I. NH2OH; II. N2H4; ... JEE Advanced level
Four sulfur oxyanions are given: thiosulfate S2O3^2-, dithionite S2O4^2-, dithionate S2O6^2- and disulfate S2O7^2- (none contains a peroxo link; O is -2). Which... JEE Advanced level
Potassium trioxalatochromate(III) is K3[Cr(C2O4)3], where oxalate is C2O4^2- (O is -2). What is the SUM of the oxidation numbers of all potassium, chromium and ... JEE Advanced level
Select the species in which the named element is in the +5 oxidation state (H is +1, Na is +1, O is -2). JEE Advanced level
Hydrogen takes the oxidation number -1 when bonded to a less electronegative element. In which of the following is H at -1? (Li, Na, Ca, Al, B take +1, +1, +2, ... JEE Advanced level
Using F = -1 and O = -2, what is (oxidation number of Xe in XeO3F2) minus (oxidation number of Xe in XeOF4)? JEE Advanced level
Select the CORRECT comparisons of oxidation numbers (O is -2, K and Na are +1, cyanide is CN-). JEE Advanced level
Potassium hexacyanidoferrate(III) contains the complex anion with six cyanide ligands (CN-). Which option correctly gives its formula, the oxidation number of F... JEE Advanced level
Match each item in Column I with the oxidation number in Column II (H is +1, Ca is +2, K is +1, F is -1, O is -2 unless the species is a superoxide). Column I: ... JEE Advanced level
Two thiosulfate ions are oxidised to one tetrathionate ion: 2S2O3^2- -> S4O6^2- + 2e-. Using the AVERAGE oxidation number of S in each ion (O is -2), by how muc... JEE Advanced level
Open-chain glucose is HOCH2-(CHOH)4-CHO (six carbons). Use the usual electronegativity rule (bond to O counts +1 per bond including double-bond counting, bond t... JEE Advanced level
What is the oxidation number of Mn in KMnO4? NEET level
In hydrogen peroxide, H2O2, what is the oxidation number of oxygen (H is +1)? NEET level
What is the oxidation number of Cr in K2Cr2O7 (O is -2, K is +1)? NEET level
What is the oxidation number of N in the ammonium ion NH4^+ (H is +1)? NEET level
What is the oxidation number of Fe in K4[Fe(CN)6] (cyanide is -1, K is +1)? NEET level
What is the oxidation number of Cl in NaOCl (Na is +1, O is -2)? NEET level
What is the AVERAGE oxidation number of S in the tetrathionate ion S4O6^2- (O is -2)? JEE Main level
What is the AVERAGE oxidation number of Fe in Fe3O4 (O is -2)? JEE Main level
What is the oxidation number of O in potassium superoxide, KO2 (the anion is O2^-)? JEE Main level
What is the AVERAGE oxidation number of N in hydrazoic acid, HN3 (H is +1)? JEE Main level
What is the AVERAGE oxidation number of C in acetic acid, CH3COOH (H is +1, O is -2)? JEE Main level
In CrO5 the structure has one Cr=O and two peroxo (O2^2-) groups, so four O atoms are -1 and one is -2. What is the oxidation number of Cr? JEE Main level
In sodium borohydride, NaBH4, hydrogen is present as hydride (-1) and Na is +1. What is the oxidation number of B? JEE Main level
Assertion: The oxidation number of oxygen in OF2 is +2. Reason: Fluorine is more electronegative than oxygen and is always assigned -1. JEE Main level
Match each species (Column I) with the oxidation number of N (Column II). Column I: P N2H4, Q NH2OH, R N2O, S NO2. Column II: 1 +4, 2 +1, 3 -1, 4 -2 (H is +1, O... JEE Main level
In which of the following does the specified atom have an AVERAGE oxidation number of exactly +2? JEE Main level
Select ALL compounds in which oxygen has oxidation number -1 (O-O link present, O2^2- for the ionic ones). JEE Main level
Find the AVERAGE oxidation number of C in carbon suboxide, C3O2 (O is -2). Give the answer to two decimal places. JEE Main level
In the thiosulfate ion S2O3^2- the structure is S-SO3 with one S (terminal) bonded only to the other S (central). Electrons of a bond between identical atoms ar... JEE Advanced level
Metal oxidation states are taken as Ba +2, Mn +4, Pb +4, Ti +4. Which listed compound must contain the peroxide ion, and what is its correct IUPAC name? JEE Advanced level
Caro's acid, H2SO5, has the structure HO-O-SO2-OH (one peroxo O-O link; H is +1). Which option gives the oxidation number of S and the number of O atoms with ox... JEE Advanced level
Arrange the Mn species by INCREASING oxidation number of Mn (use the AVERAGE for Mn3O4; K is +1, O is -2): (i) KMnO4, (ii) K2MnO4, (iii) MnO2, (iv) Mn3O4. JEE Advanced level
In sodium nitroprusside, Na2[Fe(CN)5NO], treat the nitrosyl as NO+ and each cyanide as CN^-. What is the sum of the oxidation numbers of Fe and of the nitrosyl ... JEE Advanced level
Metal oxidation numbers: Ni in Ni(CO)4 (CO neutral), Fe in K4[Fe(CN)6], Fe in K3[Fe(CN)6], Ni in K2[Ni(CN)4] (cyanide -1, K +1). What is the sum of these four o... JEE Advanced level
Arrange the oxidation numbers of O by INCREASING value in: (i) Na2O, (ii) H2O2, (iii) KO2, (iv) O2F2 (structure F-O-O-F, O-O bond shared equally, F is -1), (v) ... JEE Advanced level
Select ALL cases in which the atom has a FRACTIONAL AVERAGE oxidation number (O is -2, H is +1). JEE Advanced level
Select ALL cases in which the specified atom has oxidation number (or average) of zero (H is +1, Cl is -1, O is -2, CO neutral). JEE Advanced level
Select ALL species that contain oxygen atoms with oxidation number -1 (use the known structures: CrO5 has two peroxo groups, H2SO5 has one, S2O8^2- has one, S2O... JEE Advanced level
Select ALL rows where the name and the stated oxidation number of P are both correct. JEE Advanced level
Ammonium dichromate, (NH4)2Cr2O7, contains two NH4+ and one Cr2O7^2- (H is +1, O is -2). Find the sum of the oxidation numbers of all N atoms and all Cr atoms i... JEE Advanced level