In a titration of a solution of unknown concentration of calcium hydroxide against hydrochloric acid (concentration 0.9mol/dm3), 25cm3 of calcium hydroxide was neutralised by 22.5cm3 of hydrochloric acid. Calculate the concentration of the calcium hydroxide solution. Ca(OH)2 + 2HCl -> CaCl2 + 2H2O

Two friends at different locations want to communicate with each other by sending low energy signals. which of the following methods can they use to communicate? a) produce x-rays using colliding electrons and send them to radios, which capture sound b) send messages using infrared radiation, which travel in the form of waves c) send radio waves through intervening media like radio and television d) produce sound waves using microwaves from heated objects

If a || b and e || f, what is the value of y ?

Achange in the number of neutrons in an atom will change an blank . when the number of protons changes in an atom, a new element will form.