Explanation:
12)
a) Sodium + oxygen = ?
When sodium reacts oxygen its forms sodium oxide as a product.

b) magnesium + fluorine = ?
When magnesium reacts with fluorine its forms magnesium fluoride as a product.

13)
a) 
Decomposition of mercury(II) oxide on heating gives out mercury and oxygen gas.
b)
The electrolytic decomposition of water gives out hydrogen gas amd oxygen gas.
According to the Bronsted-Lowry definitions, an acid is any substance that donates hydrogen ions; whereas, a base is any substance that accepts hydrogen ions.
In the first reaction, water is acting as an acid because it donates a hydrogen ions.
In the second reaction, water is acting as a base because it accepts a hydrogen ion.
In the third reaction, water is again donating a hydrogen ion so it is the acid.
In the fourth reaction, water is acting as a base by accepting the hydrogen ion from the ammonium ion.
It would be C because you would do m divided by s squared and you would get 0.11 but you would round it to 0.12
Hi,
Chemistry is a branch of science that deals with the identification of the substances of which of which matters is composed.
I hope it helps!