Answer:
Chargaff's rule, also known as the complementary base pairing rule, states that DNA base pairs are always adenine with thymine (A-T) and cytosine with guanine (C-G). A purine always pairs with a pyrimidine and vice versa. However, A doesn't pair with C, despite that being a purine and a pyrimidine.
Explanation:
In these nucleotides, there is one of the four possible bases: adenine (A), guanine (G), cytosine (C), or thymine (T) (Figure below). Adenine and guanine are purine bases, and cytosine and thymine are pyrimidine bases. Chemical structure of the four nitrogenous bases in DNA✔✔
Answer : The limiting reagent is 
Solution : Given,
Moles of methane = 2.8 moles
Moles of
= 5 moles
Now we have to calculate the limiting and excess reagent.
The balanced chemical reaction is,

From the balanced reaction we conclude that
As, 2 mole of
react with 1 mole of 
So, 5 moles of
react with
moles of 
From this we conclude that,
is an excess reagent because the given moles are greater than the required moles and
is a limiting reagent and it limits the formation of product.
Hence, the limiting reagent is 
Answer: A.
B.
C.
Thus solution B is basic in nature.
Explanation:
pH is the measure of acidity or alkalinity of a solution.
pH is calculated by taking negative logarithm of hydrogen ion concentration.
pH for acidic solutions is less than 7, for basic solutions it is more than 7 and for neutral solutions it is equal to 7.
![pH=-\log [H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%20%5BH%5E%2B%5D)
![pOH=-log[OH^-]](https://tex.z-dn.net/?f=pOH%3D-log%5BOH%5E-%5D)

or ![[H^+][OH^-]=10^{-14}](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%5BOH%5E-%5D%3D10%5E%7B-14%7D)
A.
![pH=-log[H_3O^+]=-log[0.64\times 10^{-7}]=7](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D%3D-log%5B0.64%5Ctimes%2010%5E%7B-7%7D%5D%3D7)
B.
![pH=-log[H_3O^+]=-log[9.43\times 10^{-9}]=8](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D%3D-log%5B9.43%5Ctimes%2010%5E%7B-9%7D%5D%3D8)
C.
![pH=-log[H_3O^+]=-log[0.000775]=3](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D%3D-log%5B0.000775%5D%3D3)
Thus solution B is basic.
B)H20 Hydrogen+oxygen=H2O
(Water) you should know this