Please help: Noor and Hanif each poured 10cm3 of hydrochloric acid into a test tube and measured the temperature. Then they added identical pieces of magnesium ribbon. When the reaction stopped they measured the temperature again

noor's results
start temperature in Celsius: 18
end temperature in Celsius: 42

Hanif's results
start temperature in Celsius: 21
end temperature in Celsius: 45

the question: how did Noor and Hanif know when the reaction had finished?

"the periodic table is arranged in order of atomic number."

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.

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