Hey there!
We know that a chemical reaction is balanced when there is the same amount of each element on both sides of the equation.
According to the law of conservation of mass, matter cannot be created or destroyed, so we must have the same amount of each element on each side of a chemical equation.
We count the amount of each element on each side, and the products should have the same number as the reactants.
Hope this helps!
Answer : The formula unit of Sr & Cl is 
and the formula unit of Al & S is 
Explanation :
Formula unit : it is defined as the lowest number ratio of ions of an elements in an ionic compound or covalent compound.
For the formula unit of Sr & Cl, two chloride ions
are needed to neutralize the one strontium ion
.
For the formula unit of Al & S, three sulfide ions
are needed to neutralize the two aluminium ion
.
The formula unit of and are shown below.
The answer to this is solved through stochiometry: the answer is this: 0.0833mol
The principal quantum number, <span>nn</span>, designates the principal electron shell. Because n describes the most probable distance of the electrons from the nucleus, the larger the number n is, the farther the electron is from the nucleus, the larger the size of the orbital, and the larger the atom is. n can be any positive integer starting at 1, as <span><span>n=1</span><span>n=1</span></span> designates the first principal shell (the innermost shell). The first principal shell is also called the ground state, or lowest energy state. This explains why <span>nn</span> can not be 0 or any negative integer, because there exists no atoms with zero or a negative amount of energy levels/principal shells. When an electron is in an excited state or it gains energy, it may jump to the second principle shell, where <span><span>n=2</span><span>n=2</span></span>. This is called absorption because the electron is "absorbing" photons, or energy. Known as emission, electrons can also "emit" energy as they jump to lower principle shells, where n decreases by whole numbers. As the energy of the electron increases, so does the principal quantum number, e.g., n = 3 indicates the third principal shell, n = 4 indicates the fourth principal shell, and so on.
