What causes the lines in the emission spectrum for elements?

a continuous release of energy from the heated element
a quantum absorption of energy as various electrons are excited to a higher energy level
a quantum release of energy as electrons drop back to their ground state
none of the above

Consider the equilibrium system: 2icl(s) ⇄ i2(s) + cl2(g) which of the following changes will increase the total amount of of cl2 that can be produced? all of the listed answers are correct decreasing the volume of the container removing the cl2 as it is formed adding more icl(s) removing some of the i2(s)

Atrain travels 74 kilometers in 3 hours, and then 81 kilometers in 5 hours. what is its average speed?

How many atoms are there in 5.70 mol of mg