Why is the emission of an alpha particle not particularly dangerous to people?

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

Ethanol (c2h5oh) is produced from the fermentation of sucrose in the presence of enzymes. c12h22o11(aq) + h2o(g) 4 c2h5oh(l) + 4 co2(g) determine the theoretical yield and the percent yields of ethanol if 680. g sucrose undergoes fermentation and 326.5 g ethanol is obtained. theoretical _ g _ percent %

How is the atomic number of a nucleus changed by alpha decay