Hydrogen gas is explosive within the range of 4% - 75% v/v. assuming that each student in your class produces 6 l of h2 and that the lab is not ventilated, is there danger of an explosion. show your calculations to back up your answers.

In order to compute this, we must first take a couple of assumptions of:
1) The laboratory size so we can calculate its volume
2) The number of students working in the lab so we know the total gas produced
Let the lab be
11 m × 9 m × 6 m
The volume then computes to be: 
594 m³
We know that 
1 Liter is 1 dm³
1 m = 10 dm
1 m³ = 1000 dm³
Therefore, the room volume in liters is:
594,000 Liters
Let there be 30 students in the laboratory
Total gas being produced:
6 × 30
= 180 Liters
This works out to be:
0.03% of Hydrogen by volume
Therefore, there is no risk of explosion given our assumption of size and students.

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium