If there is 8 g of a substance before a physical change, how much will there be afterwards?

Asample of radium-226 will decay 1/4 of its original amount after 3200years. what is the half-life of radium-226?

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.

What is the wavelength of a 3*10^12 hz infrared wave a 3*10^20m b 1* 10^4m c 3*10^-3m d 1*10^-4 m