#### Answer

a) Uranium (235)
$\Longrightarrow$ Number of protons = 92
$\Longrightarrow$ Number of electrons = 92
$\Longrightarrow$ Number of neutrons = 143
b) Aluminum (27)
$\Longrightarrow$ Number of protons = 13
$\Longrightarrow$ Number of electrons = 13
$\Longrightarrow$ Number of neutrons = 14
c) Iron 57
$\Longrightarrow$ Number of protons = 26
$\Longrightarrow$ Number of electrons = 26
$\Longrightarrow$ Number of neutrons = 31
d) Lead (208)
$\Longrightarrow$ Number of protons = 82
$\Longrightarrow$ Number of electrons = 82
$\Longrightarrow$ Number of neutrons = 126
e)Rubidium (86)
$\Longrightarrow$ Number of protons = 37
$\Longrightarrow$ Number of electrons = 37
$\Longrightarrow$ Number of neutrons = 49
f) Calcium (41)
$\Longrightarrow$ Number of protons = 20
$\Longrightarrow$ Number of electrons = 20
$\Longrightarrow$ Number of neutrons = 21

#### Work Step by Step

a) Uranium (235):
Atomic number = Z = 92
Mass number = A = 235
Thus number of protons = Z = 92
If the atom is neutral, then number of electrons = number of protons. (Since the positive and negative charges on protons and electrons respectively are equal and thus cancel out each other)
Thus number of electrons = Z = 92
Number of neutrons = A -Z = 235 - 92 = 143
b) Aluminum (27)
Atomic number = Z = 13
Mass number = A = 27
Thus number of protons = Z = 13
If the atom is neutral, then number of electrons = number of protons. (Since the positive and negative charges on protons and electrons respectively are equal and thus cancel out each other)
Thus number of electrons = Z = 13
Number of neutrons = A -Z = 27 - 13 = 14
c) Iron (57)
Atomic number = Z = 26
Mass number = A = 57
Thus number of protons = Z = 26
If the atom is neutral, then number of electrons = number of protons. (Since the positive and negative charges on protons and electrons respectively are equal and thus cancel out each other)
Thus number of electrons = Z = 26
Number of neutrons = A -Z = 57 - 26 = 31
d) Lead (208)
Atomic number = Z = 82
Mass number = A = 208
Thus number of protons = Z = 82
If the atom is neutral, then number of electrons = number of protons. (Since the positive and negative charges on protons and electrons respectively are equal and thus cancel out each other)
Thus number of electrons = Z = 82
Number of neutrons = A -Z = 208 - 82 = 126
e) Rubidium (86)
Atomic number = Z = 37
Mass number = A = 86
Thus number of protons = Z = 37
If the atom is neutral, then number of electrons = number of protons. (Since the positive and negative charges on protons and electrons respectively are equal and thus cancel out each other)
Thus number of electrons = Z = 37
Number of neutrons = A -Z = 86 - 37 = 49
f) Calcium (41)
Atomic number = Z = 20
Mass number = A = 41
Thus number of protons = Z = 20
If the atom is neutral, then number of electrons = number of protons. (Since the positive and negative charges on protons and electrons respectively are equal and thus cancel out each other)
Thus number of electrons = Z = 20
Number of neutrons = A -Z = 41 - 20 = 21