Rhodium-105 has a half-life of 105 years. How much of a 100 gram sample would remain after 420 years?

it's c. elements are placed in rows based on how may valencies electrons have.

im not exactly sure but i think its b!

warm front forms when a moist, warm air mass slides up and over a cold air mass. as the warm air mass rises, it condenses into a broad area of clouds. a warm front brings gentle rain or light snow, followed by warmer, milder weather.

hope i !