Which one of the following, does not have a complete protein chain?

Tofu, because it doesn't have enough amino acids to make a complete chain. Unless you ate a whole lot of it, anyway. And I do mean a lot.

in a sense, you are confusing some biochemical concepts.

There are many types of proteins. And each and every food contains many different proteins. I think there are about 8 types of protein - but that is just broad categories. Each type of protein contains many different examples of specific proteins 

When you talk about foods and use the word complete proteins you are referring to the building blocks of proteins. Proteins are made up of about 20 different amino acids. Most of them can be synthesized by our bodies. But 8 (or 10) of them cannot. These are called the Essential Amino Acids. 

The idea of a complete protein is a bit of a misnomer. All food that is derived from a plant or an animal contains ALL of the amino acids. The organism couldn't even be alive unless it contains all of them. The misunderstanding comes from the fact that different foods contain different PROPORTIONS of amino acids. For instance, broccoli contains a lot more Lysine than Tryptophan. Pinto beans contain a lot more valine than brown rice. But they all contain every one of the essential amino acids. In fact, they all contain enough of every amino acid to sustain life - IF you eat adequate calories. You might have to eat 8 heads of lettuce a day but if you did you would get adequate calories and adequate protein. (think about it - how could cows exist if this wasn't true)

To answer your question, soybeans are the plant food that most closely conforms to our amino acid needs all by itself. So in your multiple-choice list the best answer is tofu. 

In your question, you made another mistake that is common. You said, "...to be stored by the body until it's needed." The body does not store protein well. its not like carbs or like fats. The body has lots of ways to store those things. Amino acids need to be utilized. Usually by the time of your next meal. Inside of the same day at the longest. Proteins that you eat are usually utilized in just a few hours. Extra proteins are broken down into amino acids and any amino acids that are "leftover" are flushed out of your body in your urine. 

And although you didn't bring it up, many people think that you need to combine plant foods in special ways to get all the essential amino acids. This is a 60-year-old myth. For years we have known that all the essential amino acids are present in all plant foods - anyone who eats adequate calories and a variety of plant foods will get all the nutrients they need.