20 mL of an approximately 10% aqueous solution of
ethylamine, CH3CH2NH2, is titrated with 0.3000 M
aqueous HCl. Which indicator would be most suitable
for this titration? The pKa of CH3CH2NH3
+ is 10.75.

(A) Thymol blue, color change from pH = 1.2 to 2.8
(B) Bromocresol green, color change from pH = 4.0 to
5.6
(C) Phenolphthalein, color change from pH = 8.0 to 10.0
(D) Alizarin yellow R, color change from pH = 10.0 to
12.0

Your question is not clear but if you can explain yourself i would be glad to .  just trying to : ))

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.