How can we find antilog using log table ?
In the Example 3.2 in the NCERT, log K_C= 15.6
For value of Antilog(15.6), how we have to proceed ?
I don't know the basic logarithm too...Please tell which formula to apply ? Do we have to use log table ?

same here

log K_c = 15.6.
Here, the log of K_c is of base 10. 
log of some number with the base 10 means the power to which 10 should be raised to get that number.
.In this case, we know the power to which 10 is raised to but we don't know the number it gives. That's where anti log comes into play.
antilog of a number = (the log base)^{the number}
In this question, the number is 15.6 and the base is 10.
So, antilog(15.6) = 10^15.6  = 10^0.6 * 10¹⁵ = antilog(0.6) * 10¹⁵

In 15.6, the part before the decimal point is called characteristic and the part after the decimal point
is called the matissa.
So in general, 
antilog of a number = antilog(mantissa) * 10^{characteristic}

Now use your log tables and go to the page for anitlogarithms. 
Look for the row of 0.600
The value is 0,3981.
But we will be taking it as 3.981. [shift one decimal to the right]
So the final answer is antilog(15.6) = 3.981 * 10¹⁵
If you use a calculator and enter 10^15.6, you'll get the same value as above.






 

 

I actually forgot to add one more thing. It would be a different way to calculate the antilog of negative numbers. Suppose we have to find antilog of -15.6. The answer is 10^-15.6. But the normal method has to be modified here. The easiest way is to split the power in such a way that you can use the rule a^m+n = a^m * aⁿ
Now do we split -15.6 like that? 
-15.6 = -16+0.4.
In general, the negative number whose antilog is to be found can be splitted as :
the number = (characteristic - 1) + (1- mantissa)

So antilog(-15.6) = 10^-15.6 = 10^-16+0.4 = 10^-16 * 10^0.4 = 10^-16 * antilog(0.4)

Now we proceed as normal.
From log tables,
antilog value for 0.400 is given as 0.2512.
As usual, shift the decimal to the  right and the antilog of 0.4 is 2.512.
Hence, antilog(-15.6) = 2.512 * 10^-16
Use this method only for finding antilog negative numbers. Use the first method for positive numbers.