Among the following,the correct statement is

One calorie is equal to (in $J$)

How many significant figures are present in the following?
$(i)$ $0.0025$ $(ii)$ $208$ $(iii)$ $5005$ $(iv)$ $126,000$ $(v)$ $500.0$ $(vi)$ $2.0034$

If the value of Avogadro number is $6.023 \times 10^{23} \ mol^{-1}$ and the value of Boltzmann constant is $1.380 \times 10^{-23} \ J \ K^{-1}$,then the number of significant digits in the calculated value of the universal gas constant is

Find the number of electrons that generate $1$ coulomb charge?

The triple point of water is $................$ $K$. (in $.16$)