Answer:
石 SEKI, SHAKU, ishi - stone
心 SHIN, kokoro - heart
了 RYOU - finish, complete, understand
雷 RAI, kaminari - thunder
工 KOU, KU - artisan, skill, work
Add a single stroke to each of these to make another character.
右 U, YUU, migi - right
必 HITSU, kanara(zu) - definite, sure
子 SHI, SU, ko - child
電 DEN - electricity
王 OU - king