B. The presence of unconformities
The first rule is to use four digits in atomic weights and consider the calculated formula or molar mass as given with four significant digits. This rule is appropriate for beginners but has some disadvantages.
The second rule is to use all digits in the recommended atomic weights and to estimate the accuracy of the result from the number of decimal places or significant digits in these.
The third rule is to use all digits in the recommended atomic weights and to calculate the absolute maximum uncertainty of the result from the recommended uncertainties of the atomic weights. The uncertainty is rounded up to one (two) significant digit(s), and the formula or molar mass is rounded to the same absolute accuracy as the rounded uncertainty.
Answer:
Examples of Chemical Changes
Burning wood.
Souring milk.
Mixing acid and base.
Digesting food.
Cooking an egg.
Heating sugar to form caramel.
Baking a cake.
Rusting of iron.
Answer:
a) No molecules of hydrogen
b) four molecules of ammonia
c) four left molecules of nitrogen.
Explanation:
The balanced reaction between nitrogen and hydrogen molecules to give ammonia molecules is:

Thus one molecule of nitrogen will react with three molecules of hydrogen to give two molecules of ammonia.
We have six molecules of each nitrogen and hydrogen in the closed container and they undergo complete reaction it means the limiting reagent is hydrogen. For six molecules of nitrogen, eighteen molecules of hydrogen will be required.
So six molecules of hydrogen will react with two molecules of nitrogen to give four molecules of ammonia.
The product mixture will have
a) No molecules of hydrogen
b) four molecules of ammonia
c) four left molecules of nitrogen.