What molecules have tetrahedral arrangement of electron pairs but is not a tetrahedral molecule.
methane
water
carbon dioxide
boron trifluoride

The correct answer is Water

Explanation:

A water molecule is composed of two hydrogen atoms and one oxygen atom.Both hydrogen atoms are linked with the single oxygen atom by covalent bonding.

         As oxygen atom contain 6 electrons in the valence orbital,among them 2 are used to form two covalent bond with two hydrogen atom and the rest 4 electrons are present as 2 lone pair of electrons.That"s why oxygen atom in H2O molecule is sp3 hybridized.According to the theory hybridization a sp3 hybridized molecule should have a tetrahedral arrangement.

        But in in case of sp3 hybridized water molecule the tetrahedral arrangement is prevented due to priority of lone pair-lone pair repulsion.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.