Explain why apparatus used for laboratory preparation of Hydrogen should be air tight and away from a naked flame?

Hint: Air contains oxygen and it is an essential component for combustion and hydrogen is very explosive in nature. So, we avoid the contact of hydrogen formed during reaction with the outer atmosphere.

Step by step explanation:
In the given question it is asked upon the laboratory preparation of Hydrogen and about its precaution that must be taken to avoid any kind of accident. Before proceeding directly to the answer let us firstly know how the hydrogen is prepared in the laboratory and what are its precautions that must be taken during this preparation.
Hydrogen gas is colorless gas and hydrogen has an atomic number of 1 so it’s a very tiny molecule. It is prepared in the lab by reacting either Hydrochloric acid or sulfuric acid with zinc granules which ultimately releases \[{H_2}\] gas. The reaction to prepare hydrogen is: - \[Zn{\text{ }} + {\text{ }}2HCl \to {\text{ }}ZnC{l_2} + {\text{ }}{H_2}\]
From this the hydrogen gas is prepared in the laboratory. Now during this preparation, the container and apparatus must be very tightly handled because Hydrogen is the smallest molecule among the all and it has higher chances to get leaked from any corner of the apparatus and if it comes in contact with the air, the reaction becomes highly explosive and releases large amounts of heat.
And when it is in the air and comes in contact with naked flame as well, then the reaction becomes explosive in nature and it reacts with very high flame because hydrogen is in contact with oxygen as well as flame.
The reaction that occurs is: - \[2{H_2} + {\text{ }}{O_2} \to {\text{ }}2{H_2}O\] along with about 250 kJ/mol of heat and therefore becomes violent.

Note: These types of questions are analytical based in which the complete procedure and precautions and sources of error must be known before performing any experiment. Also, the property of hydrogen gas also comes and if it is known then it can connect the property to the question and give an answer quickly.