The number of joules contained in $1\ kWh$ is:
(a) $36\times10^5\ J$
(b) $3.6\times10^7\ J$
(c) $36\times10^8\ J$
(d) $3.7\times10^7\ J$

As known $1\ kwh=1\ kw\times1\ hour$

Or $1\ kwh=1000\ watt\times60\times60\ seconds$

Or $1\ kwh=3600\times10^3\ Joule$

Or $1\ kwh=36\times10^5\ Joule$

Therefore, option (a) is correct.