Oxegan ........
explation :
Google
It is B nevermind I thought it was c but it wasn't.
<span>If thermal energy (heat) must be added to a chemical reaction in order for the reaction to take place, the reaction is endothermic. </span>
Answer:
On the placement of hydrogen and helium in the periodic system
H1=1
He2=2
Atomic mass Calcium ( Ca) = 40.078 u.m.a
40.078 g --------------- 6.02x10²³ atoms
187 g ------------------- ??
187 x ( 6.02x10²³) / 40.078 =
1.125x10²⁶ / 40.078 = 2.808x10²⁴ atoms
hope this helps!
