Final answer:
The element added to steel to increase its strength is manganese (a). Manganese improves the tensile strength of steel, which is crucial for the structural integrity of large modern buildings.
Step-by-step explanation:
The metallic element added to steel to increase its strength is manganese (a). Steels are an essential class of alloys primarily made of iron and various other elements to produce unique and desirable properties.
While chromium, nickel, and vanadium are also added to steel to enhance its strength, hardness, resistance to corrosion, and other properties, the specific element from the options provided that is recognized for strengthening steel is manganese.
Elements like chromium and nickel also contribute to the corrosion resistance and toughness of steel, while vanadium is known for increasing steel's hardness and resistance to wear.
However, manganese is particularly valued for its ability to improve the tensile strength of steel, making it an essential component in the construction of large modern structures such as skyscrapers and stadiums.