Move the decimal right until the coefficient is between 1 and 10: 0.000007 → 7 (moved 6 places right), so the exponent is −6: $7 \times 10^{-6}$. A has an exponent off by one, B has a coefficient less than 1, and D corresponds to 0.0000007. Scientific notation makes tiny measurements easier to read and compare.

Since $81=9^2$ and $100=10^2$, $98$ is between them, so $\sqrt{98}$ is between $9$ and $10$. A quick check: $9.9^2=98.01$, so $\sqrt{98}\approx9.90$ to the nearest hundredth.

$\sqrt{7}\approx2.646\Rightarrow -\sqrt{7}\approx-2.646$, which is less than $-2.5$. For the positives, $2.8<\pi\ (\approx3.142)<\tfrac{7}{2}=3.5$. On a number line: $-\sqrt{7}$ is left of $-2.5$, then $2.8$, then $\pi$, then $\tfrac{7}{2}$.

Approximate: $\sqrt{10}\approx3.162$, $\tfrac{22}{7}\approx3.143$, $3.1=3.1$, $-3.05=-3.05$, $-\pi\approx-3.142$. From greatest to least: $3.162>3.143>3.1>-3.05>-3.142$, so $\sqrt{10},\ \tfrac{22}{7},\ 3.1,\ -3.05,\ -\pi$. On the number line, the less negative number ($-3.05$) is to the right of $-\pi$.

Move the decimal right until the coefficient is between 1 and 10: 0.000000125 → 1.25 (moved 7 places), so $1.25 \times 10^{-7}$. A has a coefficient greater than 10, B has a coefficient less than 1, and D uses the wrong sign. Scientific notation is standard for wavelengths and other scientific measurements.

Since $14^2=196$ and $15^2=225$, $221$ is between them and closer to $225$, so $\sqrt{221}$ is a little less than $15$. Calculator: $\sqrt{221}\approx14.866\dots$, which rounds to $14.9$ to the nearest tenth.

$-\sqrt{16}=-4$ and $-3$ are the negatives, with $-4<-3$. For the positives: $\pi\approx3.142$, $3.4=3.4$, $\tfrac{11}{3}\approx3.667$. Thus $\pi<3.4<\tfrac{11}{3}$. So the correct order is $-4,\ -3,\ \pi,\ 3.4,\ \tfrac{11}{3}$.

Since $\sqrt{49}=7$ and $\sqrt{64}=8$, $\sqrt{50}$ is just over $7$. Calculator: $\sqrt{50}\approx7.071\dots$, which rounds to $7.07$ to the nearest hundredth.

Compute distances to $3.5$: $\left|\sqrt{12}-3.5\right|\approx|3.464-3.5|=0.036$, $\left|\pi-3.5\right|\approx|3.142-3.5|=0.358$, $\left|-\sqrt{10}-3.5\right|\approx|-3.162-3.5|=6.662$, and $\left|\tfrac{7}{2}-3.5\right|=0$. The smallest distance is $0$, so $\tfrac{7}{2}$ is exactly $3.5$ and is closest.

Approximate: $-\pi\approx-3.142$, $-3.1=-3.1$, $-\sqrt{2}\approx-1.414$, $3=3$, $\sqrt{11}\approx3.317$. On the number line, more negative numbers are less: $-3.142<-3.1<-1.414<3<3.317$. So $-\pi, -3.1, -\sqrt{2}, 3, \sqrt{11}$.