To find moles : moles= Mass (C₄H₂O₄) / RFM (C₄H₂O₄)
so moles = 147.7 / 114 = <span>1.2956mol
hope that helps </span>
The number 7 is the coefficient

multiply by (6.02 times 10^23 atoms)/(1mole, cancel out atoms)
Answer:
the answer is option (a).3
Answer: 20 mg Te-99 remains after 12 hours.
Explanation: N(t) = N(0)*(1/2)^(t/t1/2)
N(t) = (80 mg)*(0.5)^(12/6)
N(t) = 20 mg remains after 12 hours