Answer:
2Zn + 2HCI ➡️ ZnCI2 + H2
LHS of equation
Z = 2
H = 2
Cl = 2
RHS of equation
Zn = 1
Cl =2
H =2
as Zn is not equal in number of atoms on both sides of the equation, the equation does not obey the law of conservation of mass
Explanation:
the law of conservation mass states that the mass of an isolated system cannot be created nor destroyed by any chemical reaction or physical transformation. thus, there must be an equal number of atoms of an element present on both sides of the equation.
Number 3:
Chlorine, Sodium, Sulfate, Magnesium, and Calcium.
Number 4:
The salt Increases/Decreases the density.
Hope this helps you!
:)
2-7-1
<h3>Further explanation
</h3>
Electrons can move the shell up or down by releasing energy or absorbing energy
Excited electrons show higher electron transfer to the shell by absorbing energy
So it can be concluded that there are 2 conditions:
Ground state is the state of electrons filling shell with the lowest energy levels.
Excited state is the state of electrons which occupies a higher energy level
The state of excited electrons can be seen from the presence of electrons which do not fill the skin completely but fill the skin afterward
2-7-1
From its 8 electron configuration, filling 3 shells, 2 electrons in the firs shell, 7 electrons in the second shell and 1 electron in the third shell
the electrons in the third shell should fill the electrons in the second shell first according to Aufbau rule (lower energy shells)

Answer: The correct option is The properties of a noble gas.
Explanation: There are 7 periods in the periodic table.
The last element of each period are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn) and Ununoctium (Uuo).
- The electronic configuration for Helium is
. For He, The outermost electrons are 2.
- The electronic configuration for all the other elements is
( where, n = 2, 3, 4, 5, 6 and 7 respectively). For all the other gases, the outermost electrons are 8.
All these elements have stable electronic configuration and are not reactive in nature. Hence, they are considered as noble gases.
Therefore, the last element of each period always have the properties of a noble gas.