The number of electrons and the mass numbers of a series of particles are shown in the table
below (the symbols used, U to Z, are not the correct symbols for the elements).
Particle
U
V
W
X
y2+
N
Which two particles are isotopes?
A. X and Z
B. U and Y
C.W and Y
D. V and X

Electrons
12- U
10- V
10- W
10- X
10- Y
10- Z
Mass number
24-U
19-V
23- W
20- X
24- Y
22- Z