The mass of the air in the room is
50 kg.
V = lwh = 15.5 ft × 12.5 ft × 8 ft = 1550 ft³
1 ft = 12 in ×

= 30.48 cm
V = 1550 ft³ ×

= 4.39 × 10⁷ cm ³ = 4.39 × 10⁷mL = 4.39 × 10⁴ L
Mass = 4.39 × 10⁴ L ×

= 5.22 × 10⁴ g = 52.2 kg
Note: The answer can have only 1 significant figure, because that is all you gave for the height of the room.
To the correct number of significant figures, the mass of the air in the room is 50 kg.
I believe your answer is: What is the enthalpy of formation of magnesium oxide?
Hope this helps! :)
Answer:
When the solution (with phenolphthalein) changes to colorless
Explanation:
When titrating with HCl is common to add phenolphthalein as an acid-base indicator.
Phenolphthalein is pink or fucsia when added into a basic solution. On the other hand when it is in acid solutions, is colorless.
So, when titrating, the NaOH solution will be initialy pink due to the phenolphthalein and when reaching the equivalence point, that color will fade out into colorless. This is how you know you hace reached the equivalent point.