Answer:
b. a new gas is observed in the form of bubbles
Explanation:
The only statement that was evidence of a chemical reaction is a new gas is observed in the form of bubbles Any time a new substance is created, a chemical reaction has taken place.
Concave is not a type of mechanical wave because it doesn’t need a medium for propagation.
Explanation:
if it was meant for [Ar]4s²3d¹ :
1s²2s²2p⁶3s²3p⁶4s²3d¹
number of e‐ : 21
atomic number is 21.. element is scandium
ion: Sc³+