Statement-I: ${}_6{}^{14}\mathrm{C} \mathrm{and} {}_7{}^{15}\mathrm{N} \mathrm{are} \mathrm{isotones}.$

Statement-II: Isotones differ in their mass number by 1 u. 

Both statement-I and Statement-II are incorrect

Both Statement-I and Statement-II are correct

Statement-I is incorrect and Statement-II is correct

Statement-I is correct and Statement-II is incorrect