The question is incomplete, here is the complete question:
Consider the following reaction: 
In the first 15.0 s of the reaction, 1.9×10⁻² mol of O₂ is produced in a reaction vessel with a volume of 0.480 L . What is the average rate of the reaction over this time interval?
<u>Answer:</u> The average rate of appearance of oxygen gas is 
<u>Explanation:</u>
We are given:
Moles of oxygen gas = 
Volume of solution = 0.480 L
Molarity is calculated by using the equation:

So, 
The given chemical reaction follows:

The average rate of the reaction for appearance of
is given as:
![\text{Average rate of appearance of }O_2=\frac{\Delta [O_2]}{\Delta t}](https://tex.z-dn.net/?f=%5Ctext%7BAverage%20rate%20of%20appearance%20of%20%7DO_2%3D%5Cfrac%7B%5CDelta%20%5BO_2%5D%7D%7B%5CDelta%20t%7D)
Or,

where,
= final concentration of oxygen gas = 0.0396 M
= initial concentration of oxygen gas = 0 M
= final time = 15.0 s
= initial time = 0 s
Putting values in above equation, we get:

Hence, the average rate of appearance of oxygen gas is 
= 6.022 × 1020
Explanation<em>;</em>
Mole of aluminium oxide (Al2O3) is
⇒ 2 x 27 + 3 x 16
Mole of aluminium oxide = 102 g
i.e., 102 g of Al2O3= 6.022 x 1023 molecules of Al2O3
Then, 0.051 g of Al2O3 contains = 6.022 x 1023 / (102 x 0.051 molecules)
= 3.011 x 1020 molecules of Al2O3
The number of aluminium ions (Al3+) present in one molecule of aluminium oxide is 2.
Therefore, the number of aluminium ions (Al3+) present in 3.11 × 1020 molecules (0.051g) of aluminium oxide (Al2O3)
= 2 × 3.011 × 1020
=<em> 6.022 × 1020</em>
<em>hope </em><em>it </em><em>helps</em><em>_</em>
Electromagnetic wave travels faster through air than metal.
Option A
<u>Explanation:</u>
There are different kinds of wave energy. The most significant are electromagnetic and mechanical waves. The mechanical waves propagate through the medium by transfer of energy by vibrating of particles in medium.
So, the more number of particles present in the medium, the more fast the mechanical wave can propagate. So the mechanical waves travel faster in metals consisting of more number of free charge carriers. But electromagnetic waves does not need any of the medium to propagate. So it can travel faster in air than in metals.
Answer: Option (d) is the correct answer.
Explanation:
When two atoms are bonded together then it is known as a diatomic molecule.
Such as nitrogen exists as
molecule in atmosphere so, it is a diatomic molecule.
Hydrogen also exists as
molecule in atmosphere so, it is also a diatomic molecule. Also, bromine is a diatomic molecule because it exists as
molecule into the atmosphere.
But helium exists as He molecule as it has 2 electrons so, as per the octet rule it's s-shell is completely filled. Hence, it is stable and exists as a monoatomic molecule into the atmosphere.
Thus, we can conclude that out of the given options, helium is not a diatomic molecule.
Answer:
2.32
Explanation:
For the resolution of the problem one of the laws of Charles - Gay Lussac must be used, in which it is stated that if a<em> certain amount of gas is kept at a constant volume (as in this case), its pressure will be directly proportional to its absolute temperature.</em> Mathematically, it can be written as follows:
⇒to constant V
In the case of the statement, that we have an initial system (P₁ and T₁) and an final system (P₂ and T₂), the equation can be written:

It can be rearranged to clear P₂ which is what needs to be calculated, then:

It would only be necessary to <em>convert the temperature units from ° C to K</em>, to have the absolute temperature values. If T (K) = t (° C) + 273.15, then:
T₁ = 0 + 273.15 = 273.15 K
T₂ = 150 + 273.15 = 423.15 K
Now, you can replace the values to the equation and calculate P₂
≅ 2.32 atm
As the statement requests the result with three significant figures and no units, the answer is that<em> the final pressure is 2.32</em>