Encryption Keys (Understand Code)

Hello Experts,
Here is the partial code of my Encryption program which encrypts the data in 256 bits.  Here I am trying to understand the code to take it to next level.

1. What is the meaning of Encryption.m_Key = new byte[0x20] ?  Why it is [0x20], not [0x22] ?
2. What is the meaning of Encryption.m_IV = new byte[0x10] ? Why it is [0x10], not [0x11] ?
3. How line 1 and 2 are related?  I mean to say byte[0x20] and byte[0x10]. Does the 2nd one needs to be 10 byte long because 1st one is 20 bytes?
4. Why do we use m_IV?  Does the name matter here?

Please answer the above questions if possible.  FYI, I am not allowed to post the code.  I modified it as little as possible for explaining things.

Thank you very much in advance.

            public void GenerateKey()
            {
                  Encryption.m_Key = new byte[0x20];
                  Encryption.m_IV = new byte[0x10];
                  
                  RegistryKey key2 = Registry.LocalMachine.OpenSubKey("XXXXXXX").OpenSubKey("SubKey2");
                  if (key2 != null)
                  {
                        RegistryKey key3 = key2.OpenSubKey("SubKey3");
                        if (key3 != null)
                        {
                                      .
                                      .
                                      .
                        }
                  }
            }