17.Unbalanced and incomplete chemical equations are given. Fill up the gaps by selecting from the formulae of the molecules given in brackets. Also balance the given equations. a) Zn + 2HCl → --a-- + H 2 b) 2Mg + --b-- → 2MgO c) 4Al +3O 2 → c

a) ZnCl₂; Zn + 2HCl ⟶ ZnCl₂ + H₂

b) MgO;  2Mg + O₂ ⟶ 2MgO

c) Al₂O₃; 4Al + 3O₂ ⟶ 2Al₂O₃

Explanation:

a) Zn + HCl

(i) Identify the missing compound

Zn + HCl ⟶ a +H₂

We have Zn and Cl on the left but not on the right.

a = ZnCl₂

(ii) Write the balanced equation

Zn + 2HCl ⟶ ZnCl₂ + H₂

b) 2Mg

(i) Identify the missing element

2Mg + b ⟶ 2MgO

We have O on the right but not on the left.

b = O₂

(ii) Write the balanced equation

2Mg + O₂ ⟶ 2MgO

c) 4Al + 3O₂

(i) Identify the missing compound

4Al + 3O₂ ⟶ c

We have Al and O on the left but not on the right.

The missing substance must be a compound of Al and O₂.

c = Al₂O₃

(ii) Write the balanced equation

4Al + 3O₂ ⟶ 2Al₂O₃

they are both synthetic elements

explanation:

d

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.