Why use \" in arduino code?
Why there are (escapes) &quot; ---&quot; used in the code? Why can't we use the string normally?

Because escapes are required.
In C &quot; means 'The start or end of a string', but \&quot; means 'A double-quote character'.
There has to be a way to distinguish a double-quote character from a string delimiter so the compiler knows which is which. Without escapes your string would look like:
char json[] = &quot;{&quot;sensor&quot;:&quot;gps&quot;,&quot;time&quot;:1351824120,&quot;data&quot;:[48.756080,2.302038]}&quot;; 

and the compiler would find the end of the string at the second &quot;, and then a load of junk before it finds the end-of-statement ; character. It can't work out what sensor&quot;:&quot;gps&quot;,&quot;time&quot;:1351824120,&quot;data&quot;:[48.756080,2.302038]}&quot; is supposed to be, since it isn't in the string, but after it.