Strong electrolytes are substances that exists in solutions as only ions. These substances dissociate 100% in solutions. Strong acids, strong bases, and salts are all examples of strong electrolytes.  is a strong acid.  is a salt.  is a salt.  is a weak acid_.   is a weak base. Therefore the answer is three.

Ionic compounds are chemical compounds made of charged ions held together by forces called ionic bonding. Ionic bonds are formed by transfers of valance electrons, which create charged atoms (ions) which are attracted to each other because they have opposite charges. This is not be confused with covalent bonding, in which atoms form an attraction by sharing electrons.

 contains a positively charged  ion and negatively charged  ion which form an ionic bond.  contains two positively charged  ions and a negatively charged  ion which form an ionic bond. , , and  are all examples of molecules that contain covalent bonds. None of them contains any charged ions. The answer is therefore "two," referring to the  and  molecules.

Hydrogen bonding occurs between hydrogen and a very electronegative atom, which is usually fluorine, oxygen, or nitrogen. Thus, hydrogen bonding does not occur in .

An electrolyte is a substance that when dissolved in a solution breaks up into ions. More specifically, an electrolyte breaks up into cations (positively charged ions) and anions (negatively charged ions). While strong electrolytes break up 100% into anions and cations, weak electrolytes break apart significantly less. Less than 10% of a weak electrolyte ionizes at all in solution. That means the 90%–99% of the weak electrolyte's molecules do not ionize. This is because the intermolecular forces that form between the solution and the weak electrolyte's molecules are not stronger than the intramolecular forces holding the molecule together. While solutions containing weak electrolytes contain both ions formed from the weak electrolyte ions and molecules of the weak electrolyte, they contain mostly molecules of the weak electrolyte.

 cannot receive another proton  because then it would become , which does not exist. All of the other answer choices are fine:

 has a molar mass of approximately 40 g/mol, meaning that there is 0.01 mol of it in the solution. Sodium hydroxide is a strong base and completely dissociates in water. Its concentration in the solution is  . This means that the concentration of  ions is  and . Thus, the pH of the solution is 11.

First, note that the molecule does not have a charge, meaning that the oxidation numbers of each atom must add up to zero. Hydrogen has an oxidation number of  and oxygen has an oxidation number of . Thus, if we call the oxidation number of nitrogen , we can get the equation . Solving this gives , so the oxidation number of nitrogen is  in this molecule.

Statement II is false: reduction is a gain of electrons. Looking at statement I, the ion's charge would decrease by 3 in becoming a metal, which suggests that the ion gains 3 electrons. Thus, it is undergoing reduction.

The formula for the equilibrium constant is the product of the concentration of the products divided by the product of the concentration of the reactants. Since none of the reactants or products have coefficients, no exponents are needed in the expression. The phases do not affect the equilibrium constant in this example.

In order to calculate the empirical formula of vanillin from the given percent composition data, we can pretend we have a 100 g sample vanillin and from there estimate how many grams of each element make up the sample. For example, Vanillin is  carbon; therefore, the estimated sample would contain 66.3 g of carbon. After doing this for each of the elements vanillin contains, we can use the atomic mass of carbon to find how many moles of carbon make up the sample. We then do the same for each element that composes vanillin. See calculations below:

After finding the number of moles of each element in the hypothetical 100 g sample, we look at the ratio between the moles of each element by dividing all the samples by smallest number of moles. After finding the ratios of the samples, we are able to use the empirical formula of the vanillin by rounding up to the nearest whole number for each sample. If the ratios are not close enough to round up (like in this example), we multiply the ratios all by the same number until each number is equal to a whole number nicely. See calculations below:

We need whole numbers, so multiply each of the resulting numbers by 3 to get rid of the fractions.

This gives us  as the final answer.