Magma can push through holes or cracks in the crust of the volcano, causing a volcanic eruption. Which is when magma flows or erupts onto earth's surface, which is what you call lava (whenever it goes onto the earths surface).
A volcano is created when hot molten rock, ash and gases escape from an opening in the Earth's surface. The molten rock and ash solidify as they cool, forming the distinctive volcano shape shown here. As a volcano erupts, it spills lava that flows downslope. Hot ash and gases are thrown into the air.
Given information : Sample of 
We need to find the moles of Chlorine in the given sample.
We can say that we need to find moles from the given atoms.
Relation between mole and atom is given by : 
Where
is Avogadro number.


On solving the above equation , atoms(unit) gets cancelled out and we get 0.0286 mol.
In the given sample the moles of Chlorine (Cl) is 0.0286 mol , so option A is correct.