Which notation represents one part per billion?

Which notation represents one part per billion?

• A. 1x10^-12
• B. 1x10^-6
• C. 1.0x10^-9
• D. 1x10^-3

Answer: (C)

One part per billion means one unit in a billion units, which is 1/1,000,000,000. In scientific notation that’s 1×10^−9, so the notation 1.0×10^−9 matches ppb. The other options represent different tiny scales: 1×10^−6 is one part per million, 1×10^−12 is one part per trillion, and 1×10^−3 is one part per thousand.

One part per billion means one unit in a billion units, which is 1/1,000,000,000. In scientific notation that’s 1×10^−9, so the notation 1.0×10^−9 matches ppb. The other options represent different tiny scales: 1×10^−6 is one part per million, 1×10^−12 is one part per trillion, and 1×10^−3 is one part per thousand.