Which of the following statements about diamond are correct ? 1. It is used as a gem in jewellery because of its ability to reflect light 2. It is a good conductor of electricity 3. It is used for cutting glass, marble stones and other hard materials 4. It is used for drilling of rocks Select the correct answer using the code given below :

Diamond is an allotrope of carbon with unique physical properties. Statement 1 is correct because diamond's high refractive index of 2.42 [2] and high dispersion cause total internal reflection and 'fire', making it a prized gem. Statement 2 is incorrect; unlike graphite, diamond is an insulator with very high electrical resistivity (10^12 - 10^13 ̩m) , as it lacks free electrons [1]. Statement 3 is correct because diamond is the hardest known natural substance [1], allowing it to cut glass, marble, and other hard materials. Statement 4 is correct as industrial-grade diamonds are used in specialized drill bits for rock excavation and core sampling due to their extreme durability. Therefore, statements 1, 3, and 4 are accurate, while statement 2 is false.

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > QUESTIONS > p. 150
2. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Allotropes of carbon > p. 61