Answer: The correct option is C ( is very hard and burns cleanly).
Explanation:
COAL is a form of rock that is made up of mostly carbon amongst other elements which includes sulphur, nitrogen, hydrogen and oxygen. There are different types of coal which include:
--> anthracite ( 90% carbon)
--> bituminous coal ( 70-90% carbon)
--> lignite ( 60- 70% carbon) and
--> peat (60 % carbon).
Anthracite is the type of coal that contains the highest carbon content ( 90% carbon). This makes it very hard and is often a times referred to as HARD COAL. Anthracite is a higher quality coal for domestic and open fire heating. This is because it contains less impurities than other type of coal and thereby making it to BURN CLEANLY avoiding atmospheric pollution.
Remember this:
1) n is principal quantum number and represents the energy level.
2) l is the second quantum number and represent the type of orbital.
3) l can take values from 0 to n - 1
4) each number of l is associated with a type of orbital. This table shows the equivalence:
l number type of orbital
0 s
1 p
2 d
3 f
With that, you can tell that n = 2 permits l = 0 and 1, which is orbitals s and p.
Therefore, the answer is the option D) s, p.
Answer:

Explanation:
Hello,
In this case, the only source of hydrogen is in the 6 molecules of water, therefore, the atoms of hydrogen, by applying stoichiometry with the Avogadro's number is:

Best regards.
Answer: 4 hours
Explanation:
It takes the kayak 1 minute to travel 35 meters.
Divide the total (8400m) by the amount of meters per minute (35m)

Now convert into hours. (Remember that 1h has 60min)