In the modern long form of the periodic table, how many groups and how many periods are present?

Introduction / Context:
This question checks your basic factual knowledge of the structure of the modern periodic table. The number of groups and periods is a standard fact that appears in almost every chemistry textbook. Knowing this structure is essential because later concepts such as periodic trends, block classification, and element families are all defined in terms of groups and periods.

Given Data / Assumptions:

• The periodic table referred to is the modern long form periodic table.
• Groups are vertical columns, periods are horizontal rows.
• We need to recall the total number of each.
• Options present various combinations such as 18 and 7, 18 and 8, and so on.

Concept / Approach:
In the long form periodic table, elements are arranged according to increasing atomic number. There are 18 vertical columns called groups and 7 horizontal rows called periods. Groups represent families of elements with similar valence electron configurations, while periods represent elements with the same number of electron shells. This arrangement allows clear display of s, p, d and f block elements.

Step-by-Step Solution:
Step 1: Recall that the modern periodic table consists of 7 horizontal rows. Step 2: These rows are called periods and are numbered from 1 to 7. Step 3: Recall that there are 18 vertical columns called groups. Step 4: Groups are numbered from 1 to 18 in the modern IUPAC system, replacing older A and B group notations. Step 5: Therefore the correct pair is 18 groups and 7 periods. Step 6: Match this with the options provided; it corresponds to option 18 groups and 7 periods.

Verification / Alternative check:
You can quickly verify by looking at any standard periodic table chart. The top row shows elements from hydrogen to helium, which is period 1. Subsequent periods go down to period 7, which includes the actinides. For groups, you can count from the alkali metals as group 1 through to the noble gases as group 18. This universal structure confirms the answer 18 groups and 7 periods.

Why Other Options Are Wrong:
Options suggesting 8 periods are incorrect because there are currently only 7 recognised periods in the modern table. Options suggesting 16 groups do not match the IUPAC numbering, which clearly defines 18 groups. The combination 7 groups and 18 periods reverses the reality and is also incorrect. Thus, only the combination 18 groups and 7 periods matches the established structure of the modern periodic table.

Common Pitfalls:
Some students confuse older notations in which main groups were labelled using Roman numerals and letters A and B. They may also confuse the number of periods with the highest principal quantum number of known elements, but the correct count in basic chemistry is fixed at 7 periods. Remember that the periodic table you see on classroom walls or in textbooks uses 18 numbered groups and 7 numbered periods.

Final Answer:
The modern periodic table has 18 groups and 7 periods.