After 3 half lifes go by, there are 26g of Sodium-24 left. The parent sample of Sodium-24 is grams.

NUMBERS ONLY FOR THIS ANSWER

Blank 1:

208 grams

Explanation:

Half life is the time it takes for a sample to reduce to half it's initial concentration.

In this question, 3 half lives go by. This is given as;

Let original mass be represented by x

First Half life;

Starting mass = X

Remaining mass = X/2

Second Half life;

Starting mass = X/2

Remaining mass = (X/2) / 2 = x/4

Third Half life;

Starting mass = X/4

Remaining mass = (X/4) / 2 = X/8

Since 26g was left, it means;

X/8 = 26

X = 26 * 8  = 208 grams

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.