Predict the formulae of the stable binary compounds that would be formed by the combination of the following pairs of elements.
(a) Lithium and oxygen
(b) Magnesium and nitrogen
(c) Aluminium and iodine
(d) Silicon and oxygen
(e) Phosphorus and fluorine
(f) Element $71$ and fluorine

Hint: For solving this type questions, first find out the family in which the element belongs and then make an approach for finding the formula. Try to find out the number of electrons required by the element to attain the noble gas configuration.

Complete step by step answer:
For such types of problems, we should know about the electronic configuration of the given element first and then what type of family in which the element belongs. Then, we have to find out the number of valence electrons (i.e. the electrons present in the outermost shell of an element) that are required by the element to fulfil the stable noble gas configuration and then by cross multiplication, you will get your formulae.
So, let us go through each option.
(a) As we know, lithium ($Li$) is an alkali metal having one valence electron when it is combined with oxygen ($O$), which is a group sixteen element and has two valence electrons, will form $L{{i}_{2}}O$.

(b) Alkaline earth metal magnesium ($Mg$) having two valence electrons when is combined with nitrogen ($N$), which is a group five element with three valence electrons will form $M{{g}_{3}}{{N}_{2}}$.

(c) Aluminium is a group thirteen element having three valence electrons, when combined with iodine (a halogen with one valence) will form $Al{{I}_{3}}$.

(d) Silicon is a group fourteen element having a valence of four, when combined with group sixteen element oxygen (having valence of two) will form $Si{{O}_{2}}$.

(e) Group fifteen element phosphorus with valence of three or five, when is combined with fluorine having valence of one and is a halogen, will form $P{{F}_{3}}$ or $P{{F}_{5}}$.

(f) Here in this option, it is given that the element (consider as E) is having an atomic number $71$. So, it will have an electronic configuration $(Xe)4{{f}^{14}}5{{d}^{1}}6{{s}^{2}}$ having three electrons in its valence shell. When this element combines with fluorine (a halogen with valence of one) will form$E{{F}_{3}}$.

Note: The electrons which are present in the outermost shell or valence shell of an atom or an element will tell about the valence of the atom and the electrons further required to occupy a stable configuration that of noble gas (these electrons are referred to as the valence electrons). So, you should know about the valence and configuration of an element to predict the formulae when it gets combined with another atom.