Which definition describes a half-life?

the time required for half of a radioactive sample to decay.

the time required for half of a radioactive sample to become unstable.

the time required for all of a radioactive sample to change because of heat.

the time required for all of a sample to break down due to pressure change.

At a temperature of 393 k, the temperature of a sample of nitrogen is 1.07 atm what will the pressure be at a temperature of 478 k

Me i dont know what to do! the table compares the number of electrons in two unknown neutral atoms. comparison of electrons atom number of electrons a 10 d 11 use this information to determine the number of valence electrons in the atoms. which of the following correctly compares the stability of the two atoms? both are unreactive. both are highly reactive. a is unreactive and d is reactive. a is reactive and d is unreactive.

Ageochemist examines a piece of metal that he found in the soil. he performs tests to identify the metal from its density, electrical conductivity, and melting point. which statement best describes his investigation? a. he is determining physical properties that are sufficient to identify the metal.b. he is determining chemical properties that are sufficient to identify the metal.c. he is determining physical properties that are insufficient to identify the metal.d. he is determining chemical properties that are insufficient to identify the metal.