solution

Q1)

   1:public class StringLength {
   2:    public static void main(String[] args) {
   3:        int sum = 0;
   4:        for(int i = 0; i < args.length; i++) {
   5:            sum+=args[i].length();
   6:        }
   7:        System.out.println(sum);
   8:    }
   9:}

Q2)

   1:public class RemoveDigit {
   2:    public static String removeDigit(String s) {
   3:        char[] array = s.toCharArray();
   4:        String temp = "";
   5:        for(int i = 0; i < array.length; i++) {
   6:            if(!Character.isDigit(array[i])) {
   7:                temp = temp + array[i];
   8:            }
   9:        }
  10:        return temp;
  11:    }
  12:    
  13:    public static void main(String[] args) {
  14:        for(int i = 0; i < args.length; i++) {
  15:            System.out.print(removeDigit(args[i]) + " ");
  16:        }
  17:    }
  18:}

Q3) string.length() and array.length are correct.

Q4) (i),(iii),(iv). are correct.

(ii) begins with a digit, which is not allowed

(v) and (vi) contains characters other than _, $

(vii) is a reserved keyword.
Q5) 101
Q6) Refer to my notes.
Question 7)

public class Match{
    public static void main(String[] args) {
        if(args.length >= 2) {
	    char[] charArray = args[0].toCharArray();
	    boolean done; 
	    for(int i = 1; i < args.length; i++) {
		done = false;
		for(int j = 0; j< charArray.length; j++) {
		    if(args[i].indexOf(charArray[j]) != -1) {
			if(!done) { 
			    done = true;
			    System.out.print(args[i] + " ");
			}
		    }
		}
	    }
       }
    }
}

A solution using break

public class Match{
    public static void main(String[] args) {
        if(args.length >= 2) {
	    char[] charArray = args[0].toCharArray();
	    for(int i = 1; i < args.length; i++) {
		for(int j = 0; j<charArray.length; j++) {
		    if(args[i].indexOf(charArray[j]) != -1) {
			    System.out.print(args[i] + " ");
			    break;
		    }
		}
	    }
       }
    }
}