Answer: Option A. -> Yes

scanf is a function that reads data with specified format from a given string stream source. 
scanf("%d",&number);

atoi() convert string to integer. 
var number;
number = atoi("string");

Answer: Option A. -> Yes

string.h is the header in the C standard library for the C programming language which contains 

macro definitions, constants, and declarations of functions and types used not only for string 

handling but also various memory handling functions.

Answer: Option A. -> Yes

itoa() takes the integer input value input and converts it to a number in base radix. The resulting number a sequence of base-radix digits.
Example:

/* itoa() example */
#include<stdio.h>
#include <stdlib.h>
int main ()
{
int no;
char buff [50];
printf ("Enter number: ");
scanf ("%d",&no);
itoa (no,buff,10);
printf ("Decimal: %s\n",buff);
itoa (no,buff,2);
printf ("Binary: %s\n",buff);
itoa (no,buff,16);
printf ("Hexadecimal: %s\n",buff);
return 0;
}
Output:
Enter a number: 1250
Decimal: 1250
Binary: 10011100010
Hexadecimal: 4e2

Answer: Option B. -> No

The C standard library consists of a set of sections of the ISO C standard which describe 

a collection of header files and library routines used to implement common operations, 

such as input/output and string handling, in the C programming language. The C standard 

library is an interface standard described by a document; it is not an actual library of software 

routines available for linkage to C programs.

Answer: Option A. -> True

g = strcmp(s1, s2); returns 0 when the strings are equal, a negative integer when s1 is less than s2, or a positive integer if s1 is greater than s2, that strcmp() not only returns -1, 0 and +1, but also other negative or positive values(returns difference between the first non-matching pair of characters between s1 and s2).
A possible implementation for strcmp() in "The Standard C Library".

int strcmp (const char * s1, const char * s2)
{
for(; *s1 == *s2; ++s1, ++s2)
{
if(*s1 == 0)
return 0;
}
return *(unsigned char *)s1 < *(unsigned char *)s2 ? -1 : 1;
}

Answer: Option B. -> False

fwrite() - Unformatted write in to a file.
fscanf() - Formatted read from a file.

Answer: Option A. -> True

The ftell() function shall obtain the current value of the file-position indicator for the stream pointed to by stream.
Example:

#include<stdio.h>
int main(void)
{
FILE *stream;
stream = fopen("MYFILE.TXT", "w+");
fprintf(stream, "This is a test");
printf("The file pointer is at byte %ld\n", ftell(stream));
fclose(stream);
return 0;
}

Answer: Option A. -> True

FILE - a structure containing the information about a file or text stream needed to perform 

input or output operations on it, including:
=> a file descriptor, the current stream position,
=> an end-of-file indicator, 
=> an error indicator, 
=> a pointer to the stream's buffer, if applicable

fpos_t - a non-array type capable of uniquely identifying the position of every byte in a file.
size_t - an unsigned integer type which is the type of the result of the sizeof operator.

Answer: Option B. -> aaaaa

for(i=1; i<=5; i++) Here the for loop runs 5 times.

Loop 1: 
scanf("%c", &c); Here we give 'a' as input. 
printf("%c", c); prints the character 'a' which is given in the previous "scanf()" statement. 
ungetc(c, stdin); "ungetc()" function pushes character 'a' back into input stream.

Loop 2: 
Here the scanf("%c", &c); get the input from "stdin" because of "ungetc" function. 
printf("%c", c); Now variable c = 'a'. So it prints the character 'a'. 
ungetc(c, stdin); "ungetc()" function pushes character 'a' back into input stream.

This above process will be repeated in Loop 3, Loop 4, Loop 5.

Answer: Option A. -> True

C string is a character sequence stored as a one-dimensional character array and 

terminated with a null character('', called NULL in ASCII). 
The length of a C string is found by searching for the (first) NULL byte.