If the edge length of a NaH unit cell is 488 pm, what is the length of Na-H bond if it crystallises in the fcc structure ?

If the edge length of a NaH unit cell is 488 pm, what is the length of

1.	If the edge length of a NaH unit cell is 488 pm, what is the length of Na-H bond if it crystallises in the fcc structure ?
Answer» 122 pm 244 pm 488 pm 976 pm Solution :NaH has fcc structure SIMILAR to that of NACL. Thus, edge length of NaH=`2(r_(Na^+)+(r_H^(-))` i.e., `2(r_(Na^+)+r_(H^-))`=488 pm `THEREFORE r_(Na^+)+r_(H^-)`=244 pm, which is Na-H BOND length