Answer:
Explanation:
When we react Hydrochlorid Acid with zinc we have the following reaction:
2HCl(aq) + Zn(s) --> ZnCl2(aq) + H2(g)
The hydrogen gas formed is lost to the environment, so we can affirme that in the start we have the mass for all the H, Cl and Zn atoms in the solution, but after the reaction occurs, we have only the mass for the Cl and Zn atoms.
That's why the mass is less than the original.
The law that the student was told is only applied to closed environments.
Each element shows the group and period they are through the number of energy level and valence electron in which can determine their place in the periodic table.
Answer:
Flood barriers
Explanation:
Many towns in flood-prone areas are surrounded by flood barriers that are built to hold back rising water during seasonal highs.
- Flood barriers are water resistant walls that are used to prevent breaking water during a high period of inundation from their channels.
- They are usually vertical artificial structures which can be temporary or permanent.
- They help to hold or contain the flood water during the high season.
- These walls prevents flood plains and other nearby areas from getting flooded during the rainy season.
Given question is incomplete. The complete question is as follows.
Balance the following equation:

Answer: The balanced chemical equation is as follows.

Explanation:
When a chemical equation contains same number of atoms on both reactant and product side then this equation is known as balanced equation.
For example, 
Number of atoms on reactant side:
H = 5
P = 1
O = 6
Ca = 1
Number of atoms on product side:
H = 6
P = 2
O = 9
Ca = 1
In order to balance this equation, we will multiply
by 2 on reactant side and we will multiply
by 2 on product side. Hence, the balanced chemical equation is as follows.
