Exams › JEE Main › General

The recommended concentration of fluoride ion in drinking water is up to 1 ppm as fluoride ion is required to make teeth enamel harder by converting [3Ca 3 (PO 4 ) 2 .Ca(OH) 2 ] to :

1. [CaF 2 ]
2. [3(CaF 2 ).Ca(OH) 2 ]
3. [3Ca 3 (PO 4 ) 2 .CaF 2 ]
4. [3{Ca(OH) 2 }.CaF 2 ]

Correct answer: [3Ca 3 (PO 4 ) 2 .CaF 2 ]

Related JEE Main General questions

• A charge Q is uniformly distributed over a long rod AB of length L as shown in the figure. The electric potential at the point O lying at a distance L from the end A is - L A O L B
• A sonometer wire of length 1.5 m is made of steel. The tension in it produces an elastic strain of 1%. What is the fundamental frequency of steel if density and elasticity of steel are 7.7 × 10 3 kg/m 3 and 2.2 × 10 11 N/m 2 respectively ?
• A projectile is given an initial velocity of ) j ˆ 2 i ˆ ( + m/s, where i ˆ is along the ground and j ˆ is along the vertical. If g = 10 m/s 2 , the equation of its trajectory is -
• A uniform cylinder of length L and mass M having cross-sectional area A is suspended, with its length vertical, from a fixed point by a massless spring, such that it is half submerged in a liquid of density σ at equilibrium position. The extension x 0 of the spring when it is in equilibrium is - (Here k is spring constant)
• The graph between angle of deviation ( δ ) and angle of incidence (i) for a triangular prism is represented by -
• Diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is 2 × 10 8 m/s, the focal length of the lens is -

⚔️ Practice JEE Main General free + battle 1v1 →