Answer:
The molecular formula of estradiol is:
.
Explanation:
Molar mass of of estradiol = M= 272.37 g/mol
Let the molecular formula of estradiol be 
Percentage of an element in a compound:

Percentage of carbon in estradiol :

x = 18.0
Percentage of hydrogen in estradiol :

y = 24.2 ≈ 24
Percentage of oxygen in estradiol :

z = 2
The molecular formula of estradiol is: 
There are two naturally occurring isotopes of gallium: mass of Ga-69 isotope is 68.9256 amu and its percentage abundance is 60.11%, let the mass of other isotope that is Ga-71 be X, the percentage abundance can be calculated as:
%Ga-71=100-60.11=39.89%
Atomic mass of an element is calculated by taking sum of atomic masses of its isotopes multiplied by their percentage abundance.
Thus, in this case:
Atomic mass= m(Ga-69)×%(Ga-69)+X×%(Ga-71)
From the periodic table, atomic mass of Ga is 69.723 amu.
Putting the values,

Thus,

Rearranging,

Therefore, mass of Ga-71 isotope is 70.9246 amu.
The answer is 2 electrons.
The electron configuration of calcium is 2:8:8:2
Calcium has two electrons in its outermost shell. These are its valence electrons and are the ones used in bonding with other elements. Valence electrons of an atom are those electrons that are in its outer energy shell or that are available for bonding.
Calcium is a metal. When metals react with non-metals, electrons are transferred from the metal atoms to the non-metal atoms forming ions. The resulting compound is known as an ionic compound.
For example, when calcium metal reacts with chlorine gas, calcium gives up its two valence electrons and Chlorine accepts them resulting in a new substance called calcium chloride in which the two elements have ended up forming ionic bonds.
Answer : The amount of heat released is, -121.04 KJ
Solution : Given,
Enthalpy of reaction,
= -890 KJ
Mass of methane = 6 g
Molar mass of methane = 44 g/mole
First we have to calculate the moles of methane.

The given balanced reaction is,
From the balanced reaction we conclude that
1 mole of methane releases heat = -890 KJ
0.136 moles of methane releases heat =
Therefore, the amount of heat released is, -121.04 KJ