Answer:
2HCL
Explanation:
Both the elements have 2 so when placing the 2 infront ,it'll distribute/ apply to both
1. ₉¹⁹F
2. Mg(OH)₂
3. 2H₂ + O₂ ⇒ 2H₂O
<h3>Further explanation</h3>
1. Fluorine, atomic number : 9 , mass number = 19
Symbol : ₉¹⁹F
protons=electrons=atomic number = 9
neutrons = mass number - atomic mass

Configuration : [He] 2s² 2p⁵
2. Magnesium hydroxide is an ionic compound and is a strong base consisting of 2 ions:
Positive ion: Magnesium: Mg²⁺
negative ion: Hydroxide: OH⁻
The charges of the two are crossed, so that the compound becomes:
Mg(OH)₂
3. Reaction :
H₂ + O₂ --------> H₂O
give coefficient :
aH₂ + bO₂ --------> H₂O
H, left = 2a, right 2⇒2a=2⇒a=1
O, left = 2b, right 1⇒2b=1⇒b=0.5
Reaction becomes :
H₂ + 0.5O₂ --------> H₂O x 2
2H₂ + O₂ --------> 2H₂O
Each type of
mineral has a chemical composition that is unique such as its chemical composition
and the arrangement of atoms. For example, the mineral hematite is Fe2O3. There
are two atoms of iron (Fe) and three atoms of oxygen (O).
IVA: nonmetal/other metals VIIA:halogens VIII: Nobel Gases