Starting with 100 grams of uranium-238, after one half life has gone by, how many grams of uranium-238 will remain?
a._12.5 grams
b._25 grams
c._50 grams
d._100 grams

Answer : The correct option is, (C) 50 grams

Solution :

Formula used :

where,

a = amount of reactant left after n-half lives = ?

= Initial amount of the reactant = 100 g

n = number of half lives  = 1

Putting values in above equation, we get:

Therefore, the amount of uranium-238 remain will be, 50 g

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer