Question: Which block is used to offset the  periodic table?
About the article "Periodic table", section "Blocks".

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The different regions of the periodic table are sometimes referred to as "blocks" in recognition of the sequence in which the electron shells of the elements are filled.
Each block is named according to the subshell in which the "last" electron notionally resides.
The s-block comprises the first two groups (alkali metals and alkaline earth metals) as well as hydrogen and helium.
The p-block comprises the last six groups which are groups 13 to 18 in IUPAC (3A to 8A in American) and contains, among other elements, all of the metalloids.
The d-block comprises groups 3 to 12 in IUPAC (or 3B to 2B in American group numbering) and contains all of the transition metals.
The f-block, usually offset below the rest of the periodic table, comprises the lanthanides and actinides.
Helium is placed next to hydrogen instead of on top of neon because it is part of the s2 group.
In addition to the blocks listed in this table, there is a hypothetical g-block which is not pictured here.
g-block elements can be seen in the expanded extended periodic table.
Also, lutetium and lawrencium are placed under scandium and yttrium to reflect their status as d-block elements. 
Although both hydrogen and helium are in the s-block, neither of them behaves similarly to other s-block elements.
Their behaviour is so different from the other s-block elements that there is considerable disagreement over where these two elements should be placed in the periodic table.
Hydrogen is sometimes placed above lithium, above carbon, above fluorine, above both lithium and fluorine (appearing twice), or left floating above the other elements and not assigned to any group in the periodic table.
Helium is almost always placed above neon (which is in the p-block) in the periodic table as a noble gas, although it is occasionally placed above beryllium due to their similar electron configuration. 
The p-block is one of two blocks in the periodic table to contain nonmetals (although the s-block only contains two nonmetals, hydrogen and helium).
As such, it has some of the most diverse properties of any region in the periodic table.
The metals in this region of the periodic table are, in general, softer and have lower melting points than transition metals.
The p-block is the only region of the periodic table to contain metalloids.
In general, the farther one goes to the right, and the farther one goes up in the p-block, the less metallic the elements get; the metalloids form a diagonal line from the upper left to the lower right of the p-block. 
A block of the periodic table of elements is a set of adjacent groups.
The term appears to have been first used (in French) by Charles Janet.
The respective highest-energy electrons in each element in a block belong to the same atomic orbital type.
Each block is named after its characteristic orbital; thus, the blocks are:  s-block  p-block  d-block  f-block  g-block (hypothetical) The block names (s, p, d, f and g) are derived from the quality of the spectroscopic lines of the associated atomic orbitals: sharp, principal, diffuse and fundamental, the rest being named in alphabetical order from g onwards, omitting j.
Blocks are sometimes called families.
The following is the order for filling the "subshell" orbitals, according to the Aufbau principle, which also gives the linear order of the "blocks" (as atomic number increases) in the periodic table: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, ... For discussion of the nature of why the energies of the blocks naturally appear in this order in complex atoms, see atomic orbital and electron configuration.
The "periodic" nature of the filling of orbitals, as well as emergence of the s, p, d and f "blocks" is more obvious, if this order of filling is given in matrix form, with increasing principal quantum numbers starting the new rows ("periods") in the matrix.
Then, each subshell (composed of the first two quantum numbers) is repeated as many times as required for each pair of electrons it may contain.
The result is a compressed periodic table, with each entry representing two successive elements: