Could somebody please help this is really hard

The answers to your questions are given below

Explanation:

1. 3 Na2SO4

Molecules of Na2SO4 = 3

Na (sodium) = 3 x 2 = 6

S (sulphur) = 3 x 1 = 3

O (oxygen) = 3 x 4 = 12

2. 4 Pb(NO3)2

Molecules of Pb(NO3)2 = 2

Pb (lead) = 4 x 1 = 4

N (nitrogen) = 4 x 2 x 1 = 8

O (oxygen) = 4 x 3 x 2 = 24

it's c (engineer's do their work with mechanical stuff not on any living being)