The atomic number=5
The mass number=11
Further explanation
In the following element notation,
X = symbol of elemental atom
A = mass number
= number of protons + number of neutrons
Z = atomic number
= number of protons = number of electrons, on neutral elements
So for The atomic notation for a particular atom of Boron :
₅B¹¹
Z=5=atomic number
A=11=mass number