48.024 grams is the correct mass, because helium has an atomic mass of 4.002g, so all you have do is multiply 12 by 4.002 to get your mass of 12 helium atoms.

**Answer : The number of marbles lined up across the circumference of the earth can be, marbles**

**Explanation :**

**First we have to calculate the diameter of tiny marble.**

r = radius of marble = 0.25 mm

**Now we have to calculate the number of marbles can be lined up across the circumference of the earth.**

**Given:**

Circumference of the earth distance =

**conversion used:**

Number of marbles can be lined up = marbles

**Thus, the number of marbles lined up across the circumference of the earth can be, marbles**

I think is feet because you mostly you feet the centimeters

**The minus sign in ' –285.8 kJ/mol' indicates that the formation of water is an exothermic process**. In an exothermic process heat is released by the system.

On the contrary, a positive value of the heat of formation indicates that the process is endothermic. In an endothermic process heat is absorbed by the system.