Answer : The energy of the photon emitted is, -12.1 eV
Explanation :
First we have to calculate the 
orbit of hydrogen atom.
Formula used :
where,
= energy of 
orbit
n = number of orbit
Z = atomic number of hydrogen atom = 1
Energy of n = 1 in an hydrogen atom:
Energy of n = 2 in an hydrogen atom:
Energy change transition from n = 1 to n = 3 occurs.
Let energy change be E.
The negative sign indicates that energy of the photon emitted.
Thus, the energy of the photon emitted is, -12.1 eV
Answer;
-Two chlorine atoms
Explanation;
A barium atom attains a stable electron configuration when it bonds with two chlorine atoms.
-Barium is an alkaline earth metal, in group two of the periodic table. Like other alkaline earth metal it has a valency of two which means it reacts by loosing two electrons.
-Chlorine on the other hand is a halogen (group seven element) it reacts by gaining an electron, thus two chlorine atoms will require two electrons. Therefore, Barium would attain a stable configuration by loosing two electrons to two chlorine atoms.
B. It is the heat required to change a gram of substance from solid to liquid
Atomic number, because the atomic number is unque to each individua element.
Answer:
<em>b</em>
<em>an increase in non-biodegradable wastes</em>
Explanation:
