Hello!
To determine [H₃O⁺], we need to apply the Henderson-Hasselback equation, since this is a case of an acid and its conjugate base:
![pH=pKa+log( \frac{[A^{-}] }{[HA]} )](https://tex.z-dn.net/?f=pH%3DpKa%2Blog%28%20%5Cfrac%7B%5BA%5E%7B-%7D%5D%20%7D%7B%5BHA%5D%7D%20%29)

Now, we use the definition of pH and clear [H₃O⁺] from there:
![pH=-log[H_3O^{+}]](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%7B%2B%7D%5D%20)
![[H_3O^{+}] = 10^{-pH} =10^{-3,84}=0,00014 M](https://tex.z-dn.net/?f=%20%5BH_3O%5E%7B%2B%7D%5D%20%3D%2010%5E%7B-pH%7D%20%3D10%5E%7B-3%2C84%7D%3D0%2C00014%20M)
So, the [H₃O⁺] concentration is
0,00014 M
Have a nice day!
Most likely the equation yields a new compound XY. This is a synthesis reaction. <span>Synthesis
reaction is a reaction where two or more substances combine to form a new
compound. It is a reaction which releases energy in the form of heat and
light. Therefore, it is an exothermic reaction.</span>
B is the correct answer since both Gondwanaland and Laurasia both technically came after pangaea
Answer:
102.807 kPa
Explanation:
There are some assumptions to be made in the answer. The air inside the balloon acts as an ideal gas at a given temperature conditions.
Using the combined ideal gas equation.

P= absolute pressure of air inside the balloon.
V= volume of air inside the balloon (6.23 L= 6.23 * 10⁻³ m³)
n= moles of gas(air). (0.250 mol)
R= Universal gas constant ( 8.314 J / mol·K)
T= Temperature in Kelvin
T= 35 + 273.15 = 308.15 K
So, 

P= 102.807 * 10³ Pa
P= 102.807 kPa