I think it’s the one that has a Br
Answer:
identify the atoms on each side
count the atoms on its side
use coefficients to increase the atoms on each side
check to make sure you have the same number of each type of atom on each side
Answer: a) 
b) 
c) 
d) 
Explanation:
General representation of an element is given as:_Z^A\textrm{X}
where,
Z represents Atomic number
A represents Mass number
X represents the symbol of an element
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons
In an atom, when neutrons or protons are lost or gains, it directly affects the mass number of an atom.
Atomic number is defined as the number of protons or number of electrons that are present in an atom.
It is characteristic of a particular element.
Atomic number = Number of electrons = Number of proton
a) Z 74, A 186: 
b) Z 80, A 201: 
c) Z 34, A 76: 
d) Z 94, A 239.: 
Answer is: <span>excited state.
In </span>excited state, hydrogen has<span> higher </span>energy<span> than in the </span>ground state (state with lowest energy). H<span>ydrogen atom has one </span>electron<span> in the lowest possible </span>orbit<span> (1s), when atom absorbs</span><span> energy</span><span>, the electron move into an excited state (quantum numbers greater than the minimum possible). </span>Electron lifetime in excited state is short.