#### Answer

(a) $^6Li$ has 3 protons
$^6Li$ has 3 neutrons
(b) $^{54}Cr$ has 24 protons
$^{54}Cr$ has 30 neutrons
(c) $^{54}Fe$ has 26 protons
$^{54}Fe$ has 28 neutrons
(d) $^{220}Rn$ has 86 protons
$^{220}Rn$ has 134 neutrons

#### Work Step by Step

(a) $^6Li$ has atomic number 3
$^6Li$ has 3 protons
Note that $6-3 = 3$
$^6Li$ has 3 neutrons
(b) $^{54}Cr$ has atomic number 24
$^{54}Cr$ has 24 protons
Note that $54-24 = 30$
$^{54}Cr$ has 30 neutrons
(c) $^{54}Fe$ has atomic number 26
$^{54}Fe$ has 26 protons
Note that $54-26 = 28$
$^{54}Fe$ has 28 neutrons
(d) $^{220}Rn$ has atomic number 86
$^{220}Rn$ has 86 protons
Note that $220-86 = 134$
$^{220}Rn$ has 134 neutrons