To find the percent error in your  value, you can use the following equation:

Doing this, we find the percent error to be 4.6%.

When chemists synthesize compounds in the lab, a theoretical yield can be calculated by using knowledge of the full, balanced chemical equation, as well as the starting amounts of all reagents including the limiting reagent. However, due to a variety of factors, the actual yield obtained at the end of the experiment is nearly always going to be lower than the theoretical yield. Some of the things that can cause this are experimental error and side reactions, among others. Thus, chemists usually take the ratio of actual yield to theoretical yield to give the percent yield.

This means that the overall process was  efficient.

The addition of so much salt (NaCl) caused the water to reach its solubility limit for NaCl. This means that no matter how much more NaCl you add to that solution or how hard you stir, it will not dissolve, and will precipitate on the bottom of the beaker. This type of solution is saturated. If the solution were unsaturated, then more salt would still be able to dissolve.

There is no special isotope that makes NaCl insoluble in water. The vigorous mixing would have separated any clumps, and if the solution was unsaturated the salt would have eventually dissolved. Magnesium chloride, another salt, is very soluble in water and would not result in the scenario described.

Each test gives us a different piece of information. The first test tells us that our compound is soluble in water. The second test tells us that heat is released when acid is added. The third test tells us that the solution turns red litmus paper blue, which means that the solution is basic. From these results, we can conclude that the compound is a water-soluble base. Now we can look at our answer options.

, , , and  are all acids.

, however, will generate cyanide ions in solution. Cyanide is basic; thus, this is our correct answer.

The target is precise because the shots are closely grouped together. However, the shots are not accurate because they are not in the middle of the target.

The target is accurate because the shots are all in the middle of the target. It is also precise because all the shots are grouped together.

The shots are not precise because they are not grouped together. However, one of the shots is in the center of the target, and thus is accurate.

Always add acid to water. You should mix solutions slowly because you run the risk of solutions spilling, which may ruin your reaction entirely. Rapid mixing can also lead to inadvertently speeding up reactions and releasing energy or heat in a dangerous manner. During dilution of acids with, water heat is released; if a small amount of water is added to a concentrated acid it has the possibility of bubbling over the counter and onto you. 

During the distillation process, the combined substances are heated until the first one boils. The substance that boils and becomes a gas is then separated from the still liquid or solid substance via condensation into a separate container. Filtration involves separating substances in solid and liquid phases through a filter paper, and is often facilitated by a vacuum. Dehydration and hydration are types of reactions where water is a product, and a reactant, respectively. Fermentation is a biochemical process that occurs under anaerobic conditions. Some organisms produce lactic acid as a byproduct of fermentation, (humans), others produce ethanol (yeast). 

When measuring any liquid in the lab, a volumetric pipet or flask is always going to be the most accurate. This makes the 9mL volumetric pipet the best choice.

There is no such thing as a 9mL watch glass. Though a 10mL syringe and graduated cylinder would be quite accurate, the 9mL volumetric pipet is more accurate, and remember the question asked for the best out of the answer choices. A beaker is very inaccurate and should only be used to transfer solutions, not to measure them.