Hi:) Anyone able to help with 1(d)? Thanks!

different number of isotopes

Explanation:

Chlorine has isotopes which are different even though they apply to the same element. Chlorine has the isotopes 35 and 37, in a 3:1 arrangement and the average of the isotopes is about 35.5(you do not round the decimal)

to calculate relative atomic mass of chlorine-35 and chlorine 37:

(occurance in nature/100)*35+ (occurance in nature/100)*37=35.5

occurance in nature for chlorine 35: 75%

Ocurance in nature for chlorine 37: 25%

so

75/100*35= 26.25

26.25 +(25/100)*37=35.5

26.25+9.25=25.5

Hope this helps!