Answer:
Absolute error 
% Error
5
Explanation:
The absolute error is the the difference in the measured value and the actual value of a quantity.
Here the actual value is
grams
The measured value is
grams
Absolute error

Percent error

Where AE stands for absolute error and AV stands for absolute value.

%
The atomic mass of Europium is 152 amu
Work:
151(0.4803) = 72.52 amu
153(0.5197) = 79.5 amu
72.5 + 79.5 = 152 amu