What is the biggest black hole ever?

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

The pressure in a fluid is affected by which characteristics of that fluid

15. which of the following is not human-caused groundwater pollution? a. water in an aquifer dissolves elements such as arsenic and mercury from surrounding rock. b. water in an aquifer is contaminated by leachate that seeps into the ground from a landfill. c. water in an aquifer becomes polluted with chemicals used in hydraulic fracturing, or fracking. d. water in an aquifer absorbs harmful bacteria from the drainage field of a septic tank.