Let's assume a car travelling toward North as positive and South as negative.

+60 + (- 100) = - 40. The car is 40 km South from point A.

Here, for any integer b,
$\frac{b}{-1}=-b$.

The product of three negative integers is negative.

For example, $-2\times -1\times -3=-6$

Let the number in blank be x.
According to question, 

x + 23 = 0
So, x = 0 - 23 = - 23

It is not always true. If one of the integers $a$ is negative and the other one $b$ is positive, then their product will be $a$ negative integer, which is less than $b$. 

Let's take an example: -4, 8

$=-4\times 8$
$=-32$
$=-32<8$

Here,
$21\times (-34)\times (-12)=8568$
$(7\times 8)-9=47$
$7\times (8-9)=-7$
$21\times (-34)\times \left(12\right)=-8568$
$\therefore -8568<-7<47<8568$

We know that addition and subtraction of integers follow closure property. So, the first two statements are correct. 
Consider four integers 3, 5, -6, -2.
The sum of these integers
= 3 + 5 + (-6) + (-2) = 0
Here, 
-8 - (-7) = -1 then,
-1 > -14
Therefore, statement iii and iv are not true.

Let the number be a. 
$\Rightarrow$ $16=\frac{-240}{a}$ 
$\Rightarrow$ $a=\frac{-240}{16}=-15$
Hence, -240 should be divided by -15 to obtain 16.

Given, x % y = x + y - xy

Therefore, x = 13 and y = 7

13 % 7 = 13 + 7 - 13 $\times$ 7 = -71

Zero has no sign. It is neither positive nor negative.