Which of the following are not decomposition reactions? A. KCIO3 → KCI + O2
B. CaO + H2O + Ca(OH)2
C. 2Mg + O2 + 2Mgo
O D. NaOH + Na2O + H2O

The following are not decomposition reactions :

B. CaO + H2O ⇒ Ca(OH)2

C. 2Mg + O2 ⇒ 2MgO

The decomposition reaction is a chemical reaction shows the decomposition  of a compound into its constituent elements or compounds

General formula :

AB⇒A+B

A. KCIO3 → KCI + O2

decomposition reaction

B. CaO + H2O ⇒ Ca(OH)2

synthesis/combination reaction

C. 2Mg + O2 ⇒ 2MgO

synthesis/combination reaction

D. 2NaOH ⇒ Na2O + H2O

decomposition reaction

i'm assuming that the correct answer is indeed the first one/ "a"..

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.