Select all pair or pairs that could form a buffer solution. Remember, a buffer has a acid and a base, but there are three specific ways to make a buffer. One way to make a buffer is to have a weak acid plus its conjugate base or a conjugate acid plus its weak base.

2nd way to make it is to have a strong acid with a weak base. But in this instance, because it's strong and weak, the weak species needs to be greater in amount, greater in concentration and then finally the last way to make one is to have a weak acid and a strong base. Again, the weak species needs to be greater in amount, so we take a look here.

In the first one we have acetic acid. This is a weak acid and hydrophoric acid, which is another weak acid. The only time a weak acid could help make a buffer is if that weak acid is with its conjugate base. Neither one of them is a conjugate of each other. Also, we could have a weak acid with a strong base. Yes, we have weak acids, but where's the strong base?

Next, we have nitric acid and ammonia. Nitric acid represents a strong acid. Ammonia represents a weak. Here strong acid, weak base is one of the three combinations. We're not talking about the amount of each, but we're assuming that the weak species is greater in amount. Therefore a buffer would be created. So this is an answer.

Next we have hydrochloric acid, which is a strong acid. Sodium chloride has one less hydrogen than hydrochloric acid, so this is the conjugate base of the strong acid. Now this does not mean it's a buffer because remember, it's a weak acid plus its conjugate base, not a strong acid and its conjugate base.

Next we have potassium hydroxide, which is a strong base with hydrocyanic acid, which is a weak acid. Again, this is one of the combinations that could create a buffer. So this is an answer.

Then finally we have sodium bromide and sodium hydroxide. Well, sodium bromide here is a strong base and the only way a strong base could help make a buffer is it linked up with a weak acid. And ABR is basically a neutral ionic salt, it's not even a weak acid so this could not work. So out of my choices, option B&D would be the pairs that could form a buffer solution.