Use your understanding of chemistry to propose an explanation for the anomaly in the trend for the hydrogen compounds of group 6a elements shown in the table below?

Water has greatest boiling and melting points because strong hydrogen bonds between water molecules (intermolecular force). That is because oxygen has largest electronegativity and smallest atomic radius of all elements in group. Other elements in this group do not form hydrogen bonds and they are gasses in room temperature, water is liquid and their boiling and melting points are lower. Boiling and melting point of hydrides gradually increases from H₂S to H₂Te because of increase of the radius and molecular mass of atoms from sulfur to tellurium, that is why intermolecular force of attraction of molecules increases. 

The answer to your question really depends on three things: how much water you have, how cold it is to start out, and how cold the things around it are. water actually freezes when it gets to 32 degrees fahrenheit (0 degrees celsius), but the time it takes to get there may be different.  let's start with the first. if you take two glasses, and fill one with a tiny bit of water, and the other about halfway, then put them both in the freezer, the one with less water will freeze first (you can try this at home, but i recommend using plastic cups and not glass ones).  now let's move on to the second part. let's say you have two glasses, and you fill one with really cold water that has been in the refrigerator, and the other with really hot water from the sink. if you put both of them in the freezer, the one that started out colder will freeze first.  for the third part, let's imagine that you have two glasses with the same amount of water in them, and the water is at the same temperature. imagine putting one outside on a really really cold day in georgia, and having a friend in alaska put one outside on the same day. since it would be so much colder in alaska, the glass of water there would freeze before yours.  so, if you took a tiny bit of really cold water in a glass, and put it outside on a cold day in alaska, it would freeze a lot faster than a big glass of hot water outside on a cold day in georgia.