The correct answer is compound.
The compounds comprise two or more elements, which are bonded together chemically, and can be dissociated, that is, distinguished by reforming and breaking the chemical bonds, by the decomposition reactions, like thermal decomposition or electrolysis. The process of decomposition generate simpler compounds or individual elements.
Answer:
260 moles of Helium
Explanation:
V = 50L
T = 20°C = (20 + 273.15)K = 293.15K
P = 125 atm
R = 0.082 L.atm / mol. K
n = ?
From ideal gas equation,
PV = nRT
P = pressure of a given gas
V = volume it occupies
n = number of moles
R = ideal gas constant
T = temperature of the gas
PV = nRT
n = PV / RT
n = (125 * 50) / (0.082 * 293.15)
n = 6250 / 24.0383
n = 260.00 moles
The child inhaled 260 moles of Helium
The first rule is to use four digits in atomic weights and consider the calculated formula or molar mass as given with four significant digits. This rule is appropriate for beginners but has some disadvantages.
The second rule is to use all digits in the recommended atomic weights and to estimate the accuracy of the result from the number of decimal places or significant digits in these.
The third rule is to use all digits in the recommended atomic weights and to calculate the absolute maximum uncertainty of the result from the recommended uncertainties of the atomic weights. The uncertainty is rounded up to one (two) significant digit(s), and the formula or molar mass is rounded to the same absolute accuracy as the rounded uncertainty.
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Mole =

Mass of Radium Hydroxide = 987g
Molar Mass of

= ((226) + (2 * 16) + (2 * 1))
= 260 g / mol
∴ Moles of <span>

= </span>

= 3.796 mols