D&D 5E Some questions on Ice Knife

[Kithas]

Could one use the Twinned spell Metamagic on the spell Ice Knife? Could one cast it as a reaction using War Caster?

Ice Knife
1st-level conjuration
Casting Time: 1 action
Range: 60 feet
Components: S, M (a drop of water or piece of ice)
Duration: Instantaneous
You create a shard of ice and fling it at one creature within range. Make a ranged spell attack against the target. On a hit, the target takes 1d10 piercing damage. Hit or miss, the shard then explodes. The target and each creature within 5 feet of the point where the ice exploded must succeed on a Dexterity saving throw or take 2d6 cold damage.


Edit; With the errata to the phb on the Draconic ancestry lvl 6, when you twin a spell like this do you only add your cha to the cold damage on one target? Or does it count as a second "casting" of the spell. The wording on the metamagic may make this clear but I am not with my phb at the moment.

 

[Voort]

Could one use the Twinned spell Metamagic on the spell Ice Knife?

According to Mike Mearls, yes.

http://www.sageadvice.eu/2015/07/01/twin-splash-dd-errata/

 

[Yunru]

Could one use the Twinned spell Metamagic on the spell Ice Knife? Could one cast it as a reaction using War Caster?

Ice Knife
1st-level conjuration
Casting Time: 1 action
Range: 60 feet
Components: S, M (a drop of water or piece of ice)
Duration: Instantaneous
You create a shard of ice and fling it at one creature within range. Make a ranged spell attack against the target. On a hit, the target takes 1d10 piercing damage. Hit or miss, the shard then explodes. The target and each creature within 5 feet of the point where the ice exploded must succeed on a Dexterity saving throw or take 2d6 cold damage.


Edit; With the errata to the phb on the Draconic ancestry lvl 6, when you twin a spell like this do you only add your cha to the cold damage on one target? Or does it count as a second "casting" of the spell. The wording on the metamagic may make this clear but I am not with my phb at the moment.

It targets only one person so yes. You add your CHA to the cold damage once, but since that's the AoE part, you can apply it to a target twice if you aim right.