Answer:
Hydrogen, <em><u>H</u></em>
Aluminum, <em><u>Al</u></em>
Cobalt, <em><u>Co</u></em>
Im not entirely sure, but they probably are not accurate enough (spillage etc.), whereas a syringe or another device is more contained and able to be effectively and scientifically measured, so there is less human error incorporated in the dosage amount. Hope this helps
Emission
I hope this helped:))
