Answer : 3. "+4"
Explanation :

Answer: C) +4 Explanation: The given compound is NaHCO3 Sodium bicarbonate which is commonly known as Baking soda. Oxidation numbers are the charges on ions. When a neutral atom loses electrons it becomes positively charged. When a neutral atom gains electrons it becomes negatively charged.   Here the C represents the oxidation state of carbon in this compound. Compounds are electrically neutral, which is why we set the sum of the oxidation states equal to zero. Sodium has a +1 oxidation state. Hydrogen has a +1 oxidation state. Oxygen has a -2 oxidation state. There are three oxygen atoms, which means the total oxidation state provided by both oxygen ions is -6. Adding up these oxidation states we get: 1 + 1 + (-6) + C = 0 -4 + C = 0 => C = 4 This means the oxidation state of carbon in this compound is +4.