a) 2 Marks
b) 2 Marks
c) 1 Mark
a) The oxygen content decreases as we move to high altitudes like mountains, so mountaineers carry oxygen cylinders with them to breathe there.
b) Burning of some material releases smoke that contains few gases and fine dust particles that is harmful, thus we feel suffocation in a closed room, where some material is burning.
c) This is done so that the harmful gases and smoke of factories are released at a height away from us.