20.
Atomic number is equivalent to its protons and electrons. :)
Answer:

Explanation:
Half time is period required to desintegrating the half of the initial number of atoms. Then, the total time is:


Answer:
molality of sodium ions is 1.473 m
Explanation:
Molarity is moles of solute per litre of solution
Molality is moles of solute per kg of solvent.
The volume of solution = 1 L
The mass of solution = volume X density = 1000mL X 1.43 = 1430 grams
The mass of solute = moles X molar mass of sodium phosphate = 0.65X164
mass of solute = 106.6 grams
the mass of solvent = 1430 - 106.6 = 1323.4 grams = 1.3234 Kg
the molality = 
Thus molality of sodium phosphate is 0.491 m
Each sodium phosphate of molecule will give three sodium ions.
Thus molality of sodium ions = 3 X 0.491 = 1.473 m
The change in temperature of the metal is 6.1°C. Details about change in temperature can be found below.
<h3>How to calculate change in temperature?</h3>
The change in temperature of a substance can be calculated by subtracting the initial temperature of the substance from the final temperature.
According to this question, a 25.0 g sample of metal at 16.0 °C is warmed to 22.1 °C by 259J of energy.
This means that the change in temperature of the metal can be calculated as:
∆T = 22.1°C - 16°C
∆T = 6.1°C
Therefore, the change in temperature of the metal is 6.1°C.
Learn more about change in temperature at: brainly.com/question/19051558
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Condensation
..when gas cool down into liquid statr its called condensation..