In an "m-ary" tree. the number of total nodes (N) is given by

N=mi + 1  ----(1)

Where,

i: Number of internal nodes

Also, in a tree, N=i + L   ----(2)

Where,

L=number of leaf nodes

Here m=2

From equation (1) and equation (2);

N = 2i + 1

2i + 1 = i + L

L = i + 1

The number of leaves are 1 plus the number of internal nodes in binary tree.

Here, given L=n, substitute above and we will get,

i = L - 1

Concept –

Option_1: A valid declaration in C.

char *str is a single value which is a pointer to a character. When used as a string in C, it is implied that subsequent characters of the string are stored in subsequent memory addresses, until the end of the string which is marked with a NULL.

Option_2: A valid declaration in C.

Char str[20] is an array of maximum 20 characters. It is similar to char *str except that there is no requirement that the last character in the array be null.

Option_3 – A valid declaration in C.

char str[40] is an array of maximum 40 characters. It is similar to char *str except that there is no requirement that the last character in the array be null.

Option_4: Not a valid declaration in C.

Declaration syntax: For structure in C and C++

struct tag_name

{

Datatype  variable_name;

struct tag_name *pointer_variable;

};

Option 2:

struct node

{

int data;

struct node*link;

}

The correct answer is main().

 Key Points

• When the operating system runs a program in C, it passes control of the computer over to that program.
• It is not possible to execute the c program without main().

 Additional Information

• In C programming, scanf() is one of the commonly used function to take input from the user.
• The scanf() function reads formatted input from the standard input such as keyboards.
• The printf() is a library function to send formatted output to the screen.
• The function prints the string inside quotations.

Answer: Option 4

Explanation: 

Consider the following example 

#include <stdio.h>
int main()
{
       int arr[10] = {1, 2, 3, 4, 5, 6, 7};

       arr++;
       return 0;
}

Here arr++; mean that

arr = arr + 1 ;

which is wrong we can not change the base address of an array and it will generate an error.
another way to do that is by using pointers.

#include <stdio.h>
int main()
{
       int arr[10] = {1, 2, 3, 4, 5, 6, 7};

       int *p = arr;

       p++;
       return 0;
}

Here int *p = arr; new pointer variable will be created which will start pointing to the first element of the array.

and p++; will cause the pointer to start pointing to the next element of the array.

Answer: Option 4

Concept: 

Full Binary Tree: 

A full binary tree is a binary tree in which each node has exactly two or 0 children.

Complete Binary Tree:

A complete binary tree is a binary tree in which

1. except last level tree is completely filled.
2. The last level is filled from left to right.

Perfect Binary Tree: 

A perfect binary tree is a binary tree in which

1. all interior node or internal nodes has 2 children.
2. all leaves are at the same level.

Balanced Binary Tree: 

A Balanced Binary tree is a binary tree in which at any node height of the left sub tree and right sub tree do not differ by more than 1.