How does atomic radius change from left to right across a period in the periodic table?
a. it tends to decrease.
c. it first increases, then decreases.
b. it tends to increase.
d. it first decreases, then increases.

Option (a) is the correct answer.

Explanation:

It is known that atoms are arranged with increasing atomic number from left to right. As a result, there will be increase in number of protons and electrons within a period, that is, from left to right.

Since protons have positive charge and electrons have negative charge so, more protons and electrons means more tightly they are attracted towards each other.

Hence, this will lead to a decrease in size of the atoms.

Therefore, we can conclude that atomic radius tends to decrease from left to right across a period in the periodic table.

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.