<span>Tums are great antiacid tablets for heartburn and indigestion. Calcium carbonate is a great chemical to treat these conditions. If it were not for calcium carbonate, then many people would have heartburn for years until they eventually died from the condition unfortunately.</span>
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Answer:
8.0 moles
Explanation:
Since the acid is monoprotic, 1 mole of the acid will be required to stochiometrically react with 1 mole of NaOH.
Using the formula: 
Concentration of acid = ?
Volume of acid = 10 mL
Concentration of base = 1.0 M
Volume of base = 40 mL
mole of acid = 1
mole of base = 1
Substitute into the equation:

Concentration of acid = 40/10 = 4.0 M
To determine the number of moles of acid present in 2.0 liters of the unknown solution:
Number of moles = Molarity x volume
molarity = 4.0 M
Volume = 2.0 Liters
Hence,
Number of moles = 4.0 x 2.0 = 8 moles
This is a combined gas law problem, according to which

where P is the pressure of the gas, V is the volume of the gas, and T is the temperature of the gas, and the subscripts 1 and 2 correspond to the initial and final conditions of the gas. In this problem, we are given the initial pressure, volume, and temperature of the gas in the balloon:
P₁ = 1.0 atm
V₁ = 1.8 L
T₁ = 295.15 K (K = °C + 273.15).
Moreover, we are given the final pressure and temperature of the gas in the balloon.
P₂ = 0.86 atm
T₂ = 281.15 K.
What we want to find is the final volume, V₂, which we can obtain by rearranging the combined gas equation to solve for V₂:

This answer has three significant figures. However, the question as written would warrant an answer that comprises one significant figure (as 8 °C has only one sig fig). In that case, the answer would be 2 L. If the answer is to be given to two significant figures, the volume would then be 2.0 L.
Because the 4s orbital is at a lower energy level.
The 4s orbital has a lower energy because it is more <em>penetrating</em> than a 3d orbital. A 4s electron can get closer the nucleus than a 3d electron, so it has a lower potential energy.
The other options are incorrect because they contradict the correct one.