This table shows

We know that as the negative exponent increases, the number becomes small. Smaller the negative exponent, larger the number.

A. Let us consider the exponents.

Lead and Silver have the same power.

Considering their decimals,

Lead is heavier than Silver as 3.44 is greater than 1.79.

∴ The heaviest element is Lead.

B. Let us consider the exponents.

Silver has 10^-25 whereas Titanium has 10^-26.

Titanium has a larger negative exponent.

∴ Titanium is lighter than Silver.

C. Let us consider the exponents of all the elements.

Hydrogen has the largest negative exponent, so it is the lightest.

Next, Titanium and Lithium have the same 10^-26.

Considering their decimals, Lithium is lighter, then comes Titanium.

Lastly, Lead and Silver have the same power 10^-25.

Considering their decimals,

Lead is heavier than Silver as 3.44 is greater than 1.79.

∴ The five elements in order of lightest to heaviest is

Hydrogen < Lithium < Titanium < Silver < Lead.