The degree sequence of a simple graph is the sequence of the degrees o...
Havel Hakimi theorem:
Arrange the degree of vertices in descending order
eg. d1, d2, d3... dn
Discard d1 and subtract '1' from the next 'di' degrees
Ex:3,2,2,1,1
discard degree 3 and subtract one from the next highest 3 degrees. It means removing a vertex of degree 3 that refers to removing 3 edges in the graphs.
So, 1,1,0,1
0,0,1,0 We should not get any negative value if it's negative, this is not a valid sequence, and Repeat it till we get the '0' sequence.
Option 1: 7, 6, 5, 4, 4, 3, 2, 1
5,4,3,3, 2, 1, 0
3, 2, 2, 1, 0, 0
1,1,0,0,0
0,0,0,0,0
Hence true.
Option 2: 6, 6, 6, 6, 3,3,2, 2
5, 5, 5, 2, 2, 1, 2 (put them in descending order)
5, 5, 5, 2, 2, 2, 1
3, 0, 0, 0, 1 (descending order)
3,1,0,0,0
0,-1,-1,0
Hence False.
Option 3: 7, 6, 6, 4, 4, 3, 2, 2
5,5, 3, 3, 2, 1, 1
4, 2, 2, 1, 0, 1
4, 2, 2, 1, 1, 0 (descending order)
1,1,0,0,0
Hence True.
Option 4: 8, 7, 7, 6, 4, 2, 1, 1
There is a degree 8 but there are only '8' vertices. A vertex cannot have an edge to itself in a simple graph. This is not a valid sequence.
Hence False.
The correct answer is II and IV.