Answer:

Explanation:
Calcium is the element of the group 2 and period 4 which means that the valence electronic configuration is
.
Chlorine is the element of the group 17 and period 3 which means that the valence electronic configuration is
.
Thus, calcium losses 2 electrons to 2 atoms of chlorine and these 2 atoms of chlorine accepts each electron to form ionic bond. This is done in order that the octet of the atoms are complete and they become stable.
Ca Cl
2 1
Cross multiplying the valency, We get, 
Thus, the formula of calcium chloride is
.
Answer is ₂₀⁴²Ca.<span>
In AZX notation
A<span> - Represents the </span>mass number of atom.
Mass number = number of
protons + number of neutrons.
<span> It is shown at
the </span>above of the left side<span> of the
atom.</span>
<span> Here it is </span>42.
<span> </span>Z - Represents the atomic number.<span>
Atomic number = number of protons.
</span><span>It is shown at the</span> bottom line of the left side of the atom.<span>
</span>Here it is 20.<span>
X - </span>Represents the symbol of the atom.<span>
<span> </span></span>Here</span> X is Ca.<span>
</span>
<em>Gasoline</em><em> </em><em>in</em><em> </em><em>water</em><em> </em><em>=</em><em> </em><em>insoluble</em><em> </em>
<em>acetone</em><em> </em><em>in</em><em> </em><em>nail</em><em> </em><em>polished</em><em> </em><em>=</em><em> </em><em>soluble</em><em> </em>
<em>salt</em><em> </em><em>in</em><em> </em><em>alcohol</em><em> </em><em>=</em><em> </em><em>soluble</em><em> </em>
<em>oil</em><em> </em><em>in</em><em> </em><em>vinegar</em><em> </em><em>=</em><em> </em><em>insoluble</em><em> </em>
<em>tawas</em><em> </em><em>in</em><em> </em><em>water</em><em> </em><em>=</em><em> </em><em>soluble</em><em>.</em><em>.</em><em>.</em>
<em>Sorry</em><em> </em><em>if</em><em> </em><em>i</em><em> </em><em>am</em><em> </em><em>incorrect</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em>
Fluorine is a nonmetal and as such it would need to take in or obtain an electron from a metal to have a stable octet, or full number of 8 electrons in its valence shell. Thus due to the indifference of electrons and protons it becomes an anion, a negatively charged ion.
Answer: 3 significant figures
Explanation: because in scientific notation only the before and after decimal number are considered but in standard form all numbers including exponents are all significant figures