Examine the following chemical equation, which shows only the reactants and one product.

Zn + 2HCl -> ZnCl2 + ?

How many H atoms must be present in the second product that is formed?

2 atoms

Explanation:

Given equation:

               Zn   +   2HCl  →  ZnCl₂   +     ?

This is a single displacement reaction. In such reaction, the reactant goes into product when one specie displacement reaction.

Here on specie displaces another in the reaction. The replacement of a metallic ion in solution by a metal atom higher in the activity series than the metal in the solution.

Since Zinc is higher than hydrogen in the acid, it will displace it and produce hydrogen gas.

The complete equation is:

             Zn   +   2HCl  →   ZnCl₂  +  H₂

1 mole of hydrogen gas  is made up of 2 ATOMS OF HYDROGEN

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance

the answer is c.the valence of the atoms combine .