You are making a temperature measurement with a lab thermometer. The increments (markings) are 1°C. You see that the temperature is about 1/3 of the way from 21°C to 22°C. How would you record this temperature? How many significant figures does it have? In what place value is the smallest certain digit? In what place value (tens, ones, tenths, etc.) is the uncertain digit?

21.3, 3 sig figs, units certain, tenths uncertain

Explanation:

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.