How much energy is absorbed when a 50.0 gram magnesium strip is heated from 45 degrees to 90 degrees

Quantity of heat energy required for change of phase= (mass) x (heat of fusion or heat of vaporization), or in equation form Q=mL. Heat of fusion=80cal/g; heat of vaporization=540 cal/g
quanity of heat energy responsible for a temperature change= (mass) x (specific heat) x (change in temperature), or in equation form,  Q=mcT

Here's another way to calculate it  

Calculate the energy absorbed by 20 grams of 100 C water that is turned into 100 C steam
Q=(20g)(540 cal/g)=10,800 cal 

I hope this helps you.

The flowers in a flower arrangement are actually alive

I’d have to say no because without oxygen in the water the fish would all be dead. so if you want to fish for dead fish, pick the ponds with the lowest oxygen concentrations.