1metre length is kept at​ 0 degree Celsius.why?

because if the temp goes up the bar will expand. A reference temperature must be chosen so that the length is standard. Zero is easy, water freezes there :)

Thank u

Great

Not,above written is not good.

Answer is,
1m is kept at 0 degree C because when temperature increases length also increases

that was helpful :)

Not good

Because it is it's initial point.