This is a straightforward unit conversion between percent and parts per million, the kind of check needed often when reading soil salinity or water quality reports.
- 40000: correct, since 1% of anything equals 10000 ppm (because a million divided by a hundred is ten thousand), so 4% works out to \(4 \times 10000 = 40000\) ppm.
- 4000: wrong, this would only be right if 1% equalled 1000 ppm, which undercounts by a factor of ten.
- 400: wrong, this treats 1% as just 100 ppm, undercounting by a factor of one hundred.
- 40: wrong, this is off from the correct value by a factor of one thousand.
Working it from the definition: percent is parts per hundred, ppm is parts per million, and a million is ten thousand hundreds, so multiplying any percent figure by 10000 gives its ppm equivalent, and 4 times 10000 is 40000.
Let's summarize:
- 1% always equals 10000 ppm.
- Multiplying the percent value by 10000 gives the ppm value directly, no other steps are needed.
So a 4% salt concentration equals 40000 ppm, which is option 1.