Which of the following instrument–measurement pairings is incorrect in basic physics and meteorology?

Introduction / Context:
In science, different instruments are designed to measure specific physical quantities. Knowing the correct pairing between an instrument and the quantity it measures is a common general knowledge and physics test topic. This question checks whether you can correctly identify which one of the listed instrument–measurement pairs is wrong or at least misleading when stated in this broad way.

Given Data / Assumptions:
- Four instruments are mentioned: hygrometer, lactometer, anemometer and seismograph.
- Each is paired with a quantity or phenomenon it is supposed to measure.
- We assume standard textbook meanings for these basic scientific instruments.

Concept / Approach:
A hygrometer is used to measure the humidity or water vapour content of the atmosphere, which is correct. An anemometer is used to measure the speed or sometimes the direction of wind, which is also correct. A seismograph records the vibrations of the earth during earthquakes and other tremors, so that pairing is also correct. A lactometer, however, is specifically designed to measure the specific gravity (or purity) of milk, not of liquids in general. Stating that it measures the specific gravity of all liquids is misleading and therefore considered incorrect in such exam questions.

Step-by-Step Solution:
Step 1: Check the hygrometer pairing. Hygrometers are well known for measuring atmospheric humidity, so option A is correct. Step 2: Check the lactometer pairing. A lactometer is used mainly to test the purity or specific gravity of milk only. Step 3: The statement that a lactometer measures the specific gravity of liquids in general is therefore too broad and inaccurate. Step 4: Check the anemometer pairing. Anemometers measure wind speed, so option C is correct. Step 5: Check the seismograph pairing. Seismographs record earthquake waves and earth tremors, so option D is also correct. Step 6: Conclude that the only incorrect or misleading pairing is the lactometer pair in option B.

Verification / Alternative check:
If you look at typical school-level tables of scientific instruments, you will find entries such as “Hygrometer – humidity,” “Anemometer – wind speed,” “Seismograph – earthquakes,” and “Lactometer – purity of milk.” None of these lists describes a lactometer as a general-purpose instrument for all liquids. This confirms that describing it as measuring the specific gravity of liquids in general is not accurate and therefore is the incorrect pairing in the list.

Why Other Options Are Wrong:
Hygrometer – water vapour content of the atmosphere: This is the correct function of a hygrometer, which measures humidity.
Anemometer – speed of the wind: This is correctly matched; anemometers measure wind speed and sometimes direction.
Seismograph – earthquakes and earth tremors: A seismograph records vibrations caused by earthquakes and similar events, so this pairing is correct.

Common Pitfalls:
Students sometimes focus only on unfamiliar names like hygrometer or seismograph and overlook the subtle error in the lactometer description. Another mistake is to think that any device measuring specific gravity can be used for all liquids, but many instruments are designed for specialised applications only. Reading each pairing carefully and recalling the exact textbook definition helps avoid such traps.

Final Answer:
The incorrect pairing is “Lactometer – specific gravity of liquids in general”, because a lactometer is specifically used for milk, not all liquids.